The prevailing view holds that the therapeutic benefit of sodium channel blockers arises from use-dependent inhibition of the transient sodium current (NaT) that is responsible for action potentials. This assumption underlies decades of drug development but has never been directly tested. Our goal was to test this assumption to guide the development of more effective sodium channel blockers. We used a mouse model of myotonia congenita, an ion channelopathy of skeletal muscle, as a system to study mechanism and efficacy of both use-dependent and closed sodium channel blockers. Intracellular current-clamp recordings were used to assess excitability during trains of stimuli. The contributions of NaT and a small, non-inactivating current (Na persistent or NaP) were directly measured with voltage-clamp recordings. At their effective concentrations none of the sodium channel blockers reduced action potential rate of rise or voltage clamp measures of NaT. In contrast at effective concentrations, all sodium channel blockers studied reduced NaP. A computational model was constructed to test the relative effects of NaT and NaP inhibition on excitability. The model confirmed that NaT block alone could not eliminate myotonia without causing hypoexcitability, whereas partial NaP block was sufficient to abolish pathological discharges while preserving normal firing. These findings redefine the therapeutic mechanism of sodium channel blockade: efficacy does not depend on blocking NaT but correlates with the inhibition of NaP. This shift in perspective reframes strategies for sodium channel drug development and suggests a novel approach to treating myotonia, neuropathic pain, cardiac arrythmia and epilepsy. KEY POINTS: At effective doses that treat hyperexcitability, Na channel blockers have little effect on the sodium current responsible for action potentials. Electrophysiologic recordings and computer simulation suggest that block of a small, persistent, sodium current (NaP) is the mechanism underlying efficacy in treating hyperexcitability. These findings suggest that screens for novel sodium channel blockers focus on block of NaP.
Sleep disordered breathing (SDB) commonly co-presents with other ventilatory impairments in patients with Alzheimer's disease (AD). Typically reported as either obstructive (OSA) or complex sleep apnoea in AD patients, SDB results in repeated bouts of hypoxia and hypercapnia from insufficient ventilation. It is thought not only that these repeated hypoxic events result in an exacerbation of AD but also that SDB and other ventilatory impairments may be a precursor to neurodegenerative diseases. Although the cause of SDB in AD patients is unclear, chemosensory drive malfunction, a response critical to maintaining homeostatic oxygen and carbon dioxide balance, may play a role. We examined basal ventilation, SDB and chemosensory function in 5XFAD mice, a beta amyloidosis model of AD which displays progressive amyloid beta (Aβ) plaque deposition by 8 months of age. We found that both male and female 5XFAD mice had nearly twice as many spontaneous apnoeas per hour compared to WT mice. Basal ventilation (V̇E) and air convection requirement (ACR) while awake were unchanged, but both hypoxic and hypercapnic ventilatory responses were impaired in 5XFAD mice. While WT mice responded to acute hypoxia with the expected increase in V̇E of ∼150%, 5XFAD mice showed a blunted increase of ∼70% with a similarly blunted hypercapnic response (∼100% increase in 5XFAD mice/∼200% increase in WT mice). Further, we found substantial Aβ deposition in the ventral lateral medulla, an important site for rhythm generation and chemosensing. Taken together, these data suggest a correlation between SDB, Aβ deposition and chemosensory deficits in 5XFAD mice. KEY POINTS: Respiratory dysfunction is common among Alzheimer's disease (AD) patients, but the nature of this dysfunction is not well understood Sleep disordered breathing (SDB) is prevalent in AD patients and is thought to contribute to disease progression 5XFAD mice, a model of beta amyloidosis, display similar respiratory deficits to humans with AD, including SDB and chemosensory changes We show that amyloid beta plaque deposition in the brainstem of 5XFAD mice localizes to regions of respiratory control Our data suggest that amyloid beta plaque deposition in brainstem respiratory control regions contributes to chemosensory dysfunction in 5XFAD mice, a pathology that could worsen SDB occurrence and potentially Aβ-dependent neuropathologies such as AD.
Itch is 'an unpleasant sensation of the skin commonly triggering an urge to scratch'. In chronic itch, the persistent itch/scratch cycle is reinforced and sustained by the intense pleasure and reward gained from scratching - sometimes after the itch has been abolished, and despite negative consequences. Scratching an itch recruits multiple areas of the limbic system that control addictive behaviours such as craving and intense pleasure seeking. It is hypothesised here that the pleasure derived from scratching is significantly influenced by small-fibre afferent input, including Aδ and C-tactile afferents. Subjective and physiological responses to acute itch and scratching were obtained from control participants, and compared with responses from IW, a participant with a well characterised large-fibre sensory neuronopathy below C3. In the forearm, IW's responses to temperature change, and physiological responses to histamine iontophoresis (wheal and axon reflex flare) match control participants. IW perceived both histamine- and cowage-induced itch, although self-reported peak intensities were lower than for controls and required a greater dose to elicit a comparable itch percept. Rough, scratching touch was rated significantly more intensely on itchy skin by both control participants and IW, and improved touch localisation in IW. Scratching an itch on the forearm is pleasurable for IW, despite the lack of large, myelinated fibres, thereby supporting the hypothesis that mechanosensitive small-fibre afferents contribute to the pleasure of scratching an itch. KEY POINTS: Both histamine- and cowage-induced itch perception are preserved in a patient with large fibre neuronopathy. Gentle, dynamic touch (optimally activating C-tactile afferents) is significantly less pleasant on itchy skin, in control participants. As expected, scratching itchy skin is pleasant in control participants. The pleasure of scratching persists in a patient lacking large myelinated (Aβ) fibres, suggesting that small-fibre afferents, that is, Aδ and/or C-fibres such as C-tactile afferents, mediate some of this sensation. These findings provide insight into the peripheral neural mechanisms underlying itch relief, and may inform approaches to chronic itch management.
Human stepping movements are known to be co-ordinated by a neural coupling of upper and lower limbs. The aim of this study was to evaluate a potential involvement of the reticulospinal system in the interlimb co-ordination by neural coupling during locomotion. During stepping electrical stimuli (ES) were applied to the right tibial nerve to assess the mechanisms underlying neural coupling of lower limbs, and loud acoustic stimuli (LAS) were released, known to activate the reticulospinal system. EMG activity of the tibialis anterior (TA) and gastrocnemius medialis (GM) of both sides was recorded during the right swing and double support phases of the step cycle and during dorsi- and plantarflexion movements of the feet. In all motor tasks the responses to both ES and LAS were modulated in the same way. The largest responses to both stimuli appeared during the right swing in the left GM and during double support in the left TA. During the right swing the left GM contributes to maintain body equilibrium over the left leg. In the double support phase the TA has to secure foot clearance for swing initiation. There was an absolute time shift in latency between responses to both ES and LAS across all tasks, compatible with a common neural structure for their generation in the brainstem. These findings suggest that reticulospinal drive is dynamically modulated and is involved in interlimb co-ordination during locomotion. KEY POINTS: Unilateral electrical stimuli (ES), applied to the right tibial nerve, were used to explore the neural coupling mechanism and its contribution to co-ordination of the legs during stepping. Loud acoustic stimuli (LAS) were applied to assess the potential involvement of the reticulospinal system in locomotor co-ordination. LAS and ES evoked similar EMG responses in the left GM during the right swing and in the left tibialis anterior (TA) during double support. A 30 ms time shift between responses to LAS and ES across all tasks is compatible with a common origin of their generation in the brainstem. Indirect evidence suggests that neural leg coupling during stepping is mediated by brainstem structures, likely the reticulospinal system.
The endogenous cannabinoid signalling system consists of G protein-coupled receptors, messengers - 2-arachidonoylglycerol (2-AG) and anandamide - and enzymatic machinery to synthesize and metabolize these messengers. Anandamide is physiologically important, but its synthesis is incompletely understood. N-Arachidonoyl-phosphatidylethanolamide phospholipase D (NAPE-PLD) synthesizes acylethanolamines, including anandamide, but how is NAPE-PLD activated? We used genetically encoded G protein-coupled receptor based (GRAB) sensors for endocannabinoids (eCBs) and immunohistochemistry to investigate. Human embryonic kidney 293 (HEK293) cells natively express Gq-coupled muscarinic M3 receptors. The muscarinic agonist oxotremorine-M stimulated the GRABeCB sensor only when HEK293 cells were cotransfected with NAPE-PLD. This signal was reduced by the NAPE-PLD inhibitor LEI401 and required both phospholipase C and internal calcium stores. Gq-coupled mGluR5 glutamate receptors effectively substitute for M3 receptors. Thus M3 receptors stimulate NAPE-PLD synthesis of acylethanolamines such as anandamide via Gq signalling pathways resembling those for 2-arachidonoylglycerol. Parasympathetic activation stimulates tearing and salivation via M3 receptors on myoepithelial cells. The cannabinoid signalling system may act as a feedback inhibitor to inhibit acetylcholine release, but the identity and source of the endogenous cannabinoid messenger are uncertain. NAPE-PLD and M3 proteins colocalize in myoepithelial cells; fatty acid amide hydrolase (FAAH) resides in glandular acinar cells. Oxotremorine-M stimulation of lacrimal or submandibular salivary glands co-cultured with HEK293-GRABeCB cells stimulated GRABeCB responses. This response was diminished by LEI401 and was also present in cells expressing GRABAEA, an anandamide-specific sensor, but not those expressing GRAB2AG. We conclude that muscarinic M3 receptors stimulate NAPE-PLD to produce anandamide in cell lines and exocrine glands. This means of stimulating anandamide synthesis may play many roles in the body. KEY POINTS: The cannabinoid signalling system plays important roles in the body and in doing so makes use of two endogenous messengers, 2-arachidonoylglycerol (2-AG) and anandamide. The regulation of anandamide synthesis is still poorly understood. This study demonstrates that muscarinic Gq-coupled GPCRs can stimulate anandamide production by activating the enzyme N-arachidonoyl-phosphatidylethanolamide phospholipase D (NAPE-PLD) and further shows that this occurs natively in salivary and lacrimal glands. Muscarinic Gq-coupled G protein-coupled receptor (GPCR) activation of NAPE-PLD to induce anandamide synthesis may play many roles in the body.
Age is the greatest risk factor for mortality and morbidity. We previously reported premature ageing in PKP2 arrhythmogenic cardiomyopathy (PKP2-ACM). However, depiction of cardiomyocyte molecular anatomy in premature ageing remains incomplete. Furthermore, the relationship between myocyte premature ageing and the molecular components of electrical homeostasis in PKP2-deficient hearts remains understudied. Therefore, we aimed to identify molecular anatomical changes of premature ageing in PKP2-deficient adult cardiomyocytes, the corresponding gene cohort and its imprint in the human electrocardiogram (ECG). We used a murine model of cardiomyocyte-specific PKP2 knockout. Molecular anatomy was resolved by expansion and structured illumination microscopy, allowing 3D-nanometric visualization, and by serial block-face scanning electron microscopy. We used omics databases to distill a subset of genes related to ageing and PKP2 deficiency containing single nucleotide polymorphisms (SNPs) with an ECG-relevant genomic signature. We found increased DNA damage and reduced abundance of transcriptionally repressed heterochromatin at the lamin-associated domain (LAD), and disrupted mitochondria ultrastructure at the intercalated disc. Genes dysregulated in ageing hearts and PKP2-deficient cells were distilled to identify those in the PKP2 human left ventricular gene network (by GTEx) that contain SNPs with an imprint in the human ECG (based on ECG GWAS). These findings indicate that in PKP2 deficiency, transcriptionally repressed heterochromatin in the LAD is vulnerable to damage, and erasing of otherwise transcriptionally inaccessible genomic regions, consistent with premature cellular ageing and transcriptional reprogramming. Multi-omics analysis indicates that reduced PKP2 expression accelerates cardiomyocyte ageing, and the age-related gene network contributes to dysfunction of cell metabolism and arrhythmia risk in PKP2-ACM. KEY POINTS: We used advanced imaging technology to unveil DNA damage and loss of heterochromatin architecture in the lamin-associated domain (LAD), and mitochondrial remodelling at the intercalated disc, as features of premature myocyte ageing in adult PKP2-deficient murine cardiomyocytes. Multi-omics analysis identified a network of genes dysregulated by ageing and by PKP2 deficiency. Cross-correlation with the ECG GWAS database found a subset of single nucleotide polymorphisms with an imprint in the human electrocardiogram. These results provide novel insight into the mechanisms of transcriptional remodelling and take an initial step toward a better understanding of the oligogenic bases of arrhythmia risk in PKP2-deficient hearts.
During running, cerebral blood flow (CBF) does not exhibit the inverted-U response observed during cycling; instead, CBF increases up to maximal exercise, despite reductions in end-tidal CO2 ( E T C O 2 ). The mechanism(s) driving this divergent response are unknown but may relate to foot strike-induced pulsatility oscillations and/or reductions in cerebrovascular CO2 reactivity (CVR). We assessed middle cerebral artery blood velocity (MCAv), E T C O 2 and MCAv pulsatility variability during an incremental running test (n = 43) and fixed workload exercise under two conditions (n = 17): (1) free running and (2) diastolic stepping, where the foot-strike was synced to the diastolic phase of the cardiac cycle. CVR was assessed (n = 12) at rest and during running. Young, healthy males and females exhibited progressive increases in the MCAv mean during incremental running (Females, Rest: 49.9 ± 11.3 cm s-1, V ̇ O 2 max : 65.7 ± 11.7 cm s-1; Males, Rest: 45.9 ± 10.8 cm s-1, V ̇ O 2 max : 67.1 ± 13.0 cm s-1; ANOVA P < 0.0001) despite reductions in E T C O 2 at higher intensities (Females, Rest: 36.41 ± 5.1 mmHg, V ̇ O 2 max : 28.2 ± 5.1 mmHg; Males, Rest: 38.6 ± 4.5 mmHg; V ̇ O 2 max : 32.5 ± 9.0 mmHg; ANOVA P < 0.0001). Diastolic stepping removed pulsatility oscillations, reducing MCAv pulsatility variability (0.14 ± 0.04 mmHg), compared with free running (0.29 ± 0.09 mmHg, P < 0.0001). However, the MCAv mean was not different (56.1 ± 8.1 cm s-1 vs. 58.0 ± 8.7 cm s-1; P = 0.211). CVR to hypocapnia decreased from rest to running (-0.79 ± 0.44 vs. -0.19 ± 0.50 cm s-1 mmHg-1; P = 0.006). Additional experiments found that hypocapnic CVR progressively decreased with increasing exercise intensity (ANOVA P = 0.0065), related to the increase in arterial pressure, but was similar during running and cycling when arterial pressure was matched (P = 0.999). These findings demonstrate that the CBF response during intense exercise is related to the prevailing arterial pressure and not modality per se, likely reflecting cerebrovascular vasoconstrictor reserve. KEY POINTS: Middle cerebral artery velocity (MCAv) increases progressively during incremental running, contrasting with the inverted-U response observed during cycling. We investigated whether this divergent response was explained by foot strike-induced pulsatility oscillations or altered cerebrovascular CO2 reactivity (CVR). Removing pulsatility oscillations, by synchronizing foot-strike with the cardiac cycle, had no effect on the MCAv mean, indicating that pulsatility oscillations do not explain the continued increase in MCAv during running. In contrast, hypocapnic CVR was markedly attenuated during high-intensity running. Follow-up experiments demonstrated that hypocapnic vasoconstrictor reserve progressively declined with increasing exercise intensity and was related to the increase in mean arterial pressure (MAP) but was similar during running and cycling when MAP was matched. These findings show that the progressive increase in MCAv during running is facilitated by a reduced responsiveness to hypocapnia, which appears related to the prevailing arterial pressure rather than modality per se. This attenuation likely reflects a reduced cerebrovascular vasoconstrictor reserve.
The Developmental Origins of Health and Disease framework proposes that adverse exposures during critical developmental windows induce epigenetic programming, increasing lifelong risk of metabolic and organ dysfunction. Maternal protein restriction (MPR) is a well-established model of early-life nutritional stress, associated with reduced nephron number early in life, in addition to renal dysfunction and hypertension during adult life. However, its long-term impact on renal ageing remains unclear. This study investigated the effects of gestational and lactational severe MPR (6% compared to 17% in controls) on the renal proteome of aged male Sprague-Dawley rats (postnatal day 540) using integrated histological, molecular and in silico approaches. MPR induced persistent renal impairment, evidenced by increased serum creatinine and tubular congestion. Proteomic analysis revealed upregulation of proteins related to small-molecule transport, stress response and energy metabolism, particularly within mitochondrial and redox pathways. By contrast, downregulated pathways involved cytoskeletal organization, vesicular transport, immune processes and post-transcriptional regulation, suggesting disruption of endomembrane dynamics. Pathway enrichment highlighted central metabolic networks, including glycolysis, pyruvate metabolism and the tricarboxylic acid cycle. Network and microRNA analyses indicated epigenetic regulation, whereas disease enrichment linked findings to metabolic and renal disorders. Nephron-segment mapping revealed region-specific alterations. Overall, MPR induces persistent renal programming, disrupting metabolism and function and increasing susceptibility to renal and metabolic diseases with ageing. KEY POINTS: Maternal protein restriction (MPR) shifts renal proteome to mitochondrial/redox metabolism. MPR causes renal histopathological lesions during ageing. The impacts of MPR are reflected in cellular and molecular alterations indicative of potential renal dysfunction. Nephron-specific and epigenetic alterations indicate targeted functional disruption. Persistent changes link early malnutrition to renal and metabolic disease risk.
Ventilatory long-term facilitation (LTF) is a persistent increase in minute ventilation ( V ̇ I ) elicited by acute intermittent hypoxia (AIH) that outlasts the stimulus duration. In humans, AIH-induced ventilatory LTF is dependent upon a sustained background of mild hypercapnia. It is not known whether changes in CO2 chemoreflex sensitivity contribute to ventilatory LTF. We hypothesised that hypercapnic AIH increases the sensitivity of peripheral, but not central, chemoreflex responses to CO2. Twenty healthy adults (age = 25 ± 4 years) completed the study. On days 1 and 2, pulmonary function testing and three hyperoxic modified CO2 rebreathing tests were performed to determine baseline central CO2 chemoreflex sensitivity. On days 3 and 4, participants were randomly assigned to hypercapnic AIH or mild hypercapnia alone. On day 5, 16 participants returned to the laboratory to complete a time-matched control (CTRL). Two CO2 rebreathing tests were performed approximately 45 and 75 min post-trial. Transient CO2 tests were used to quantify peripheral CO2 chemoreflex sensitivity pre- and post-trial. Twenty minutes after hypercapnic AIH, V ̇ I was increased 32 ± 22% versus baseline, which was significantly greater than CTRL (P < 0.001), demonstrating the presence of ventilatory LTF. Central CO2 chemoreflex sensitivity (P = 0.880) and the ventilatory recruitment threshold (P = 0.425) were unchanged after all trials. Peripheral CO2 chemoreflex sensitivity was increased 41 ± 46% after hypercapnic AIH, which was significantly greater than CTRL (P < 0.001). We conclude that enhanced peripheral CO2 chemoreflex sensitivity contributes to ventilatory LTF induced by hypercapnic AIH in awake humans. KEY POINTS: In awake humans, induction of ventilatory long-term facilitation (LTF) by acute intermittent hypoxia (AIH) requires a continuous background of mild hypercapnia; thus, ventilatory LTF may arise from increases in central and/or peripheral CO2 chemoreflex sensitivities. Central and peripheral CO2 chemoreflex sensitivity were assessed by modified hyperoxic CO2 rebreathing and transient CO2 tests, respectively, before and after hypercapnic AIH, sustained hypercapnia, and a time-matched control on separate days in 20 healthy young adults. Peripheral CO2 chemoreflex sensitivity was increased 41 ± 46% after hypercapnic AIH but no statistically significant changes were found in central CO2 chemoreflex sensitivity. These data indicate plasticity in the peripheral CO2 chemoreflex after exposure to hypercapnic AIH that contributes to ventilatory LTF in a background of mild hypercapnia.
Dietary protein restriction (PR) is a well-recognized nutritional intervention that enhances metabolic health and extends lifespan. However, the mechanisms behind this phenomenon are not well understood. Here, using genetic loss-of-function models for fibroblast growth factor 21 (Fgf21) and its obligate co-receptor β-Klotho (Klb), we demonstrate that FGF21-KLB signalling in adipocytes is indispensable for the anti-senescence effects of PR. Specifically, adipocyte FGF21 signalling preserves mitochondrial integrity, maintains an anti-inflammatory milieu and sustains nicotinamide adenine dinucleotide (NAD+) homeostasis under PR. Mechanistically, FGF21 enhances adipocyte NAD+ abundance through activation of AMP-activated protein kinase to maintain mitochondrial integrity. Additionally, high-protein feeding induces adipocyte senescence and metabolic dysfunction could be mitigated by exogenous FGF21 supplementation. Together, these findings establish adipose FGF21 signalling as a pivotal endocrine axis that couples dietary protein availability to adipocyte NAD+ metabolism and identify it as a promising target for the prevention and treatment of age-related metabolic disorders. KEY POINTS: Dietary protein restriction improves metabolic health and extends lifespan, but the mechanisms responsible for these benefits are not fully understood. Fibroblast growth factor 21 (FGF21) is a hormone strongly induced by low-protein diets and has emerged as an important regulator of metabolic adaptation. We show that FGF21 signalling specifically in adipose tissue is essential for the anti-senescence effects of dietary protein restriction. FGF21 preserves mitochondrial integrity by maintaining nicotinamide adenine dinucleotide metabolism through AMP-activated protein kinase activation. Targeting the FGF21-adipose tissue pathway may provide new strategies to prevent or treat age-related metabolic dysfunction.
Cardiac ischaemia, reduced coronary blood flow, causes significant damages to the heart, and paradoxically reperfusion, restored flow after ischaemia, often results in more severe injury. Although the mechanisms underlying cardiac ischaemia-reperfusion injury have been intensively investigated, effective therapeutic strategies applicable during reperfusion to mitigate this damage have not been established yet. To obtain more insights into the mechanisms underlying ischaemia-reperfusion injury, and to explore effective methods to relieve reperfusion injury, we developed a comprehensive mathematical model of ventricular myocyte, implementing excitation-contraction (E-C) coupling, cytosolic and mitochondrial pH regulation, pH dependence of major components of E-C coupling and cellular energy metabolism, including mitochondrial oxidative phosphorylation. The mathematical model successfully reproduced experimentally observed findings on cardiac ischaemia-reperfusion injury, such as intracellular and extracellular acidosis, cytosolic Na+ overload, cytosolic Ca2+ overload, mitochondrial dysfunction, action potential shortening and contraction failure. It was found that the reperfusion-induced exacerbation of Na+ i, Ca2+ i overloads was mainly caused by insufficient production of NADH, which is used in mitochondrial oxidative phosphorylation to synthesize ATP for Na+/K+ pump and sarcoplasmic/endoplasmic reticulum Ca2+ pump (SERCA) to expel accumulated cytosolic Na+ and Ca2+, respectively. It was suggested that the preservation of mitochondrial NADH production, attenuation of ATP consumption via SERCA or contraction for a short period or activation of the Na+/K+ pump during reperfusion mitigates reperfusion injury. KEY POINTS: Experimental data on cardiac ischaemia-reperfusion injury are available. No effective methods applicable during reperfusion were available for mitigating the injury. We developed a comprehensive cardiomyocyte model to simulate the injury. Na+ and Ca2+ overloads and contraction failure could be reproduced by the model. It was found that correcting ATP supply-consumption imbalance during reperfusion, that is, preservation of mitochondrial NADH production, attenuation of ATP consumption or activation of the Na+/K+ pump, was effective at mitigating the injury.
Central blood volume (CBV) is a key haemodynamic determinant of pulmonary diffusing capacity for carbon monoxide (DLCO) and its components, capillary blood volume (Vc) and membrane diffusing capacity (Dm,CO). However the contribution of CBV to DLCO regulation remains poorly defined. We tested the hypothesis that graded increases and decreases in CBV would elicit differential changes in DLCO, primarily driven by Vc. Eighteen healthy young adults (6 women; age: 25 [3] years; V ̇ O 2 peak : 44.5 [8.5] mL/kg/min) completed supine graded lower body positive (LBPP) and negative pressure (LBNP). DLCO, Vc and Dm,CO were assessed using the combined DLCO,NO approach at baseline and throughout LBPP and LBNP. Impedance cardiography-derived thoracic fluid content (TFC) was used as a proxy of CBV. LBPP induced a progressive increase in TFC (P < 0.001); however DLCO did not change (P = 0.589) due to a reciprocal increase in Vc (P = 0.009) and a decrease in Dm,CO (P < 0.001). In contrast LBNP elicited graded reductions in TFC (P < 0.001), DLCO (P < 0.001) and Vc (P < 0.001), with no change in Dm,CO (P = 0.610). Across LBPP and LBNP changes in TFC were associated with the corresponding changes in DLCO (P < 0.001) and Vc (P < 0.001), and Dm,CO (P < 0.044). Collectively these findings demonstrate that, in the supine position, pulmonary gas transfer is dynamically influenced by relatively small perturbations in CBV, primarily via alterations in Vc. KEY POINTS: Central blood volume (CBV) and pulmonary artery pressure are key determinants of pulmonary diffusing capacity for carbon monoxide (DLCO) and its components, capillary blood volume (Vc) and membrane diffusing capacity (Dm,CO); however the role of CBV in DLCO and its components has not yet been elucidated. During lower body positive pressure (increased CBV), DLCO did not change due to reciprocal increases in Vc and decreases in Dm,CO. During lower body negative pressure (central hypovolaemia), DLCO significantly declined, secondary to a decrease in Vc. DLCO and Vc exhibited non-linear relationships with thoracic fluid content (TFC, an index of CBV), whereas Dm,CO demonstrated a negative linear relationship with TFC. Our findings demonstrate that TFC-mediated Vc expansion alone is insufficient to augment DLCO, whereas central hypovolaemia reduces DLCO primarily via reduced capillary distention/recruitment.
Digital twins offer a way to translate rich patient data into individualized models that can be interrogated rather than merely described. In cardiac electrophysiology this approach has advanced to the point where the geometry, fibrosis, adiposity, inflammation and genotype of an individual heart can be incorporated into biophysically grounded simulations. This review accompanies The Physiological Society's annual Hodgkin-Huxley-Katz Award Lecture, presented to Dr. Natalia Trayanova in recognition of her contributions to computational cardiology and its clinical translation. It surveys the body of work developed by Dr. Trayanova and her group at Johns Hopkins University, charting the arc from the application of patient-specific heart digital twins to reveal substrate determinants of arrhythmogenesis to their translation to sudden cardiac death risk prediction and guidance of catheter ablation for ventricular tachycardia and atrial fibrillation (AF). Across ventricular disease these studies showed that scar architecture, border-zone conduction slowing, repolarization gradients, adipose infiltration and genotype-specific remodelling can govern the emergence and stability of re-entrant circuits. In the atria digital twins clarified how fibrosis distribution and driver anchoring shape AF dynamics. Taken together this body of work demonstrates that heart digital twins satisfy the operative medical criterion of informing clinical decisions that realize value, including non-invasive sudden cardiac death risk stratification, pre-procedural ventricular tachycardia (VT) ablation target prediction in a prospective Food and Drug Administration Investigational Device Exemption (FDA-IDE) clinical trial and personalized AF ablation planning. The major challenge ahead is to convert these validated but still computationally intensive technologies into scalable, continuously updated tools that can be deployed routinely in clinical care.
