Key Points A collaborative nephrologist–pharmacist telehealth clinic significantly improved difficult-to-control hypertension in patients with CKD. Reduction in systolic BP was achieved without significant and widespread worsening of renal function or change in electrolytes. Background Hypertension (HTN) is the most common chronic health condition worldwide and affects patients with CKD at increasing rates as kidney function falls. Uncontrolled BP can have a significant effect on cardiovascular disease, kidney disease progression, and mortality. We implemented an interdisciplinary team to assess the impact a fully virtual management system, on top of usual nephrology care, could have on HTN control among Veterans Administration patients with difficult to manage HTN. Methods Patients with difficult-to-control HTN were referred to a collaborative nephrology telemedicine clinic for care by a nephrologist and a clinical pharmacist. BP was managed through telephone visits conducted by the pharmacist every four to 12 weeks. Patients were sent a home BP monitor, provided education about its use, and were instructed to monitor home BP regularly. Those with at least three phone visits who had objective home BP measurements at each visit were included in the pragmatic analysis. Change in systolic BP from baseline was the primary outcome variable. Results Of the 55 patients meeting inclusion criteria, a mean reduction of 16±14 mm Hg in systolic BP and 6±7 mm Hg in diastolic BP was shown. In 12±7 months, 44% of patients achieved goal BP (<130/80) and 31% were discharged back to primary care management in an average of 8±5 months with apparent sustained effect. Conclusions An interdisciplinary team of a pharmacist and nephrologist using a virtual care model is an effective method for managing difficult-to-control HTN in this pragmatic assessment.

Chronic intermittent hypoxia (CIH) increases basal sympathetic nervous system activity, augments chemoreflex-induced sympathoexcitation, and raises blood pressure. All effects are attenuated by systemic or intracerebroventricular administration of angiotensin II type 1 receptor (AT1R) antagonists. This study aimed to quantify the effects of CIH on AT1R- and AT2R-like immunoreactivity in the rostroventrolateral medulla (RVLM) and paraventricular nucleus of the hypothalamus (PVN), central regions that are important components of the extended chemoreflex pathway. Eighteen Sprague-Dawley rats were exposed to intermittent hypoxia (FIO2 = 0.10, 1 min at 4-min intervals) for 10 hr/day for 1, 5, 10, or 21 days. After exposure, rats were deeply anesthetized and transcardially perfused with phosphate buffered saline (PBS) followed by 4% paraformaldehyde in PBS. Brains were removed and sectioned coronally into 50 µm slices. Immunohistochemistry was used to quantify AT1R and AT2R in the RVLM and the PVN. In the RVLM, CIH significantly increased the AT1R-like immunoreactivity, but did not alter AT2R immunoreactivity, thereby augmenting the AT1R:AT2R ratio in this nucleus. In the PVN, CIH had no effect on immunoreactivity of either receptor subtype. The current findings provide mechanistic insight into increased basal sympathetic outflow, enhanced chemoreflex sensitivity, and blood pressure elevation observed in rodents exposed to CIH.

New Findings What is the central question of this study? In sleep apnoea, a putative link between intermittent hypoxia and hypertension is the generation of oxygen radicals by angiotensinII and xanthine oxidase within the chemoreflex arc and vasculature. We tested whether chemoreflex control of sympathetic outflow, hypoxic vasodilatation and blood pressure are altered by angiotensin blockade (losartan) and/or xanthine oxidase inhibition (allopurinol). What is the main finding and its importance? Both drugs lowered blood pressure without altering sympathetic outflow, reducing chemoreflex sensitivity or enhancing hypoxic vasodilatation. Losartan and allopurinol are effective therapies for achieving blood pressure control in sleep apnoea. AbstractChemoreflex sensitization produced by chronic intermittent hypoxia in rats is attenuated by angiotensinII type1 receptor (AT(1)R) blockade. Both AT(1)R blockade and xanthine oxidase inhibition ameliorate chronic intermittent hypoxia-induced endothelial dysfunction. We hypothesized that treatment with losartan and allopurinol would reduce chemoreflex sensitivity and improve hypoxic vasodilatation in patients with obstructive sleep apnoea. Eighty-six hypertensive patients with apnoea-hypopnoea index 25eventsh(-1) and no other cardiovascular, pulmonary, renal or metabolic disease were randomly assigned to receive allopurinol, losartan or placebo for 6weeks. Treatment with other medications and/or continuous positive airway pressure remained unchanged. Tests of chemoreflex sensitivity and hypoxic vasodilatation were performed during wakefulness before and after treatment. Ventilation (pneumotachography), muscle sympathetic nerve activity (microneurography), heart rate (electrocardiography), arterial oxygen saturation (pulse oximetry), blood pressure (sphygmomanometry), forearm blood flow (venous occlusion plethysmography) and cerebral flow velocity (transcranial Doppler ultrasound) were measured during eupnoeic breathing and graded reductions in inspired O-2 tension. Losartan and allopurinol lowered arterial pressure measured during eupnoeic breathing and exposure to acute hypoxia. Neither drug altered the slopes of ventilatory, sympathetic or cardiovascular responses to acute hypoxia. We conclude that losartan and allopurinol are viable pharmacotherapeutic adjuncts for achieving blood pressure control in hypertensive obstructive sleep apnoea patients, even those who are adequately treated with continuous positive airway pressure.

Background: Lung transplant recipients are at high risk of developing sleep disorders such as insomnia, but the prevalence and features are currently poorly characterized within this population. Since these disorders are associated with increased morbidity and mortality, it is important to identify them to optimize the care of lung transplant recipients. We sought to evaluate the prevalence of insomnia within our university-based lung transplant clinic and determine whether a relationship exists between insomnia and exposure to immunosuppressant medications following transplantation. Methods: Participants were recruited through the University of Wisconsin Hospital and Clinics Lung Transplant Clinic (N = 125). Participants (n = 92) completed the adult sleep history questionnaire, which included the Insomnia Severity Index (ISI) to assess for insomnia (defined as ISI score >10). Cumulative tacrolimus exposure was determined in 73 patients by performing an area under the curve calculation to assess for a potential relationship between tacrolimus exposure and insomnia. Results: The prevalence of insomnia was 40% within this population. Although no difference in time since transplant was found, cumulative mean ± standard error of the mean tacrolimus exposure was significantly higher in patients with insomnia versus those without insomnia (17 190 ± 1673 ng·d/mL vs 12 130 ± 1630 ng·d/mL, respectively; P = .04). Estimated tacrolimus exposure was not greater with increasing frequency of insomnia complaints (analysis of variance P = .54). Conclusion: In our population, insomnia is common after lung transplantation, with prevalence greater than the general population. Higher cumulative exposure to tacrolimus may contribute to insomnia in this group. Future research should investigate the relationship between immunosuppressant therapy and development of sleep disorders.

We determined the effects of chronic exposure to intermittent hypoxia (CIH) on chemoreflex control of ventilation in conscious animals. Adult male Sprague-Dawley rats were exposed to CIH [nadir oxygen saturation (SpO2), 75%; 15 events/h; 10 h/day] or normoxia (NORM) for 21 days. We assessed the following responses to acute, graded hypoxia before and after exposures: ventilation (V̇e, via barometric plethysmography), V̇o2 and V̇co2 (analysis of expired air), heart rate (HR), and SpO2 (pulse oximetry via neck collar). We quantified hypoxia-induced chemoreceptor sensitivity by calculating the stimulus-response relationship between SpO2 and the ventilatory equivalent for V̇co2 (linear regression). An additional aim was to determine whether CIH causes proliferation of carotid body glomus cells (using bromodeoxyuridine). CIH exposure increased the slope of the V̇e/V̇co2/SpO2 relationship and caused hyperventilation in normoxia. Bromodeoxyuridine staining was comparable in CIH and NORM. Thus our CIH paradigm augmented hypoxic chemosensitivity without causing glomus cell proliferation.

Chronic exposure to intermittent hypoxia (CIH) elicits plasticity of the carotid sinus and phrenic nerves via reactive oxygen species (ROS). To determine whether CIH-induced alterations in ventilation, metabolism, and heart rate are also dependent on ROS, we measured responses to acute hypoxia in conscious rats after 14 and 21 d of either CIH or normoxia (NORM), with or without concomitant administration of allopurinol (xanthine oxidase inhibitor), combined allopurinol plus losartan (angiotensin II type 1 receptor antagonist), or apocynin (NADPH oxidase inhibitor). Carotid body nitrotyrosine production was measured by immunohistochemistry. CIH produced an increase in the ventilatory response to acute hypoxia that was virtually eliminated by all three pharmacologic interventions. CIH caused a robust increase in carotid body nitrotyrosine production that was greatly attenuated by allopurinol plus losartan and by apocynin but unaffected by allopurinol. CIH caused a decrease in metabolic rate and a reduction in hypoxic bradycardia. Both of these effects were prevented by allopurinol, allopurinol plus losartan, and apocynin.

CONTEXT:Complications following lung transplantation are common and significantly reduce quality of life, and increase morbidity and mortality. Increasing evidence suggests sleep disorders are prevalent following lung transplantation, but factors associated with their development are not known.OBJECTIVES:We sought to evaluate the prevalence of restless legs syndrome (RLS) in a lung transplant population and determine if a relationship exists between RLS and exposure to immunosuppressant medications.DESIGN, SETTING, AND PARTICIPANTS:Subjects were recruited through the University of Wisconsin Hospital and Clinics Lung Transplant Clinic (N = 125). Participants (N = 81) completed sleep questionnaires, including the four RLS diagnostic criteria, insomnia severity index, and Sheehan disability scale. Cumulative tacrolimus exposure was determined in 62 subjects by calculating an area under the curve (AUC) to assess for a relationship with restless legs syndrome.RESULTS:Prevalence of RLS was 35 percent. Cumulative mean ± SEM tacrolimus exposure was similar in patients with RLS versus those without RLS (17446 ± 1855 ng days/mL vs. 15303 ± 1643 ng days/mL, respectively; p = 0.42). Insomnia severity index scores (12.5 ± 1.0 vs 6.8 ± 0.7, p < 0.0001) and Sheehan disability scores (7.8 ± 1.3 vs 3.6 ± 0.6, p = 0.003) were significantly higher in those with vs those without RLS symptoms, respectively.CONCLUSIONS:Our data confirms increased prevalence of RLS following lung transplantation reported by previous studies. RLS symptoms were not related to estimated tacrolimus exposure. Predictors of RLS following lung transplantation need to be further investigated to better identify and control RLS symptoms and reduce associated insomnia and disability.

Letters to the EditorReply to JosephBarbara J. Morgan, Russell Adrian, Melissa L. Bates, John M. Dopp, and Jerome A. DempseyBarbara J. MorganJohn Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, Russell AdrianJohn Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, Melissa L. BatesJohn Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, John M. DoppJohn Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, and Jerome A. DempseyJohn Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, WisconsinPublished Online:15 Dec 2014https://doi.org/10.1152/japplphysiol.00893.2014MoreSectionsPDF (26 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor: Many thanks to Dr. Joseph (1) for requesting clarification of methods used to measure metabolic rate of the rodent in our recent study (3). Measurements of V̇o2 and V̇co2 in the rat do indeed require a great deal of precision, given that the differences between inspired and expired fractions of O2 and CO2 are very small. Dr. Joseph's letter highlights some very important potential sources of error in these measurements; however, we believe that several features of our flow-through system minimize these threats to accuracy (4). First, a single set of O2 and CO2 analyzers sample the inspired and expired air in sequential fashion. Thus there can be no differences in linearity of the sensors. Each day, a three-point calibration of these analyzers is performed using gases that bracket the range of inspired and expired O2 and CO2 that we expect under our experimental conditions based on pilot testing. The calibration routine provides us with daily assessments of linearity and drift of the two sensors. In the set of calibrations represented in our study, drift of the O2 sensor averaged 0.002, 0.016, and 0.003%, respectively, for the three calibration gases. The corresponding drift of the CO2 sensor averaged 0.002, 0.014, and 0.000%. Finally, in our system, inspired air flows directly, via a blender, from tanks of air and nitrogen to the O2 and CO2 analyzers before humidification and entry into the plethysmograph. Expired gas is dried by a dessicant prior to analysis. Thus sampling of both inspired and expired air is performed on dry gas only, which we deemed sufficient for quantifying changes in V̇o2 and V̇co2 under our varying experimental conditions. However, as detailed by Lighton and Halsey (2), for estimation of absolute values of V̇o2 and V̇co2 it is likely more accurate to incorporate measures of water vapor in both inspired and expired gases.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).AUTHOR CONTRIBUTIONSAuthor contributions: B.J.M. drafted manuscript; B.J.M. and J.A.D. edited and revised manuscript; B.J.M., R.A., M.L.B., J.M.D., and J.A.D. approved final version of manuscript.REFERENCES1. Joseph V. Comments on “Quantifying hypoxia-induced chemoreceptor sensitivity in the awake rodent” by Morgan et al. J Appl Physiol; doi:10.1152/japplphysiol.00887.2014.Link | ISI | Google Scholar2. Lighton JR, Halsey LG. Flow-through respirometry applied to chamber systems: pros and cons, hints and tips. Comp Biochem Physiol A Mol Integr Physiol 158: 265–275, 2011.Crossref | ISI | Google Scholar3. Morgan BJ, Adrian R, Bates ML, Dopp JM, Dempsey JA. Quantifying hypoxia-induced chemoreceptor sensitivity in the awake rodent. J Appl Physiol 117: 816–824, 2014.Link | ISI | Google Scholar4. Olson EB. Physiological dead space increases during initial hours of chronic hypoxemia with or without hypocapnia. J Appl Physiol 77: 1526–1531, 1994.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: B. Morgan, Univ. of Wisconsin - Madison, 1300 Univ. Ave., 5173 Medical Sciences Center, Madison, WI 53706 (e-mail: [email protected]wisc.edu). Download PDF Previous Back to Top FiguresReferencesRelatedInformationRelated articlesComments on “Quantifying hypoxia-induced chemoreceptor sensitivity in the awake rodent” by Morgan et al. 15 Dec 2014Journal of Applied Physiology More from this issue > Volume 117Issue 12December 2014Pages 1525-1525 Copyright & PermissionsCopyright © 2014 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00893.2014PubMed25512069History Published online 15 December 2014 Published in print 15 December 2014 Metrics

We evaluated several methods for characterizing hypoxic chemosensitivity in the conscious rat. Adult Sprague-Dawley rats ( n = 30) were exposed to normobaric hypoxia [inspired oxygen fraction (Fio2) 0.15, 0.12, and 0.09]. We measured ventilation (V̇e; barometric plethysmography), arterial oxygen saturation (SpO2; pulse oximeter), and oxygen consumption and carbon dioxide production (V̇o2and V̇co2; analysis of expired air). Linear regression analysis was used to define stimulus-response relationships. Testing was performed on 2 days to assess day-to-day reproducibility. Exposure to graded, steady-state hypoxia caused progressive reductions in SpO2that were, for any given Fio2, quite variable (SpO2range, 20–30%) among individuals. Hypoxia produced progressive increases in V̇e caused by increases in both tidal volume (VT) and breathing frequency. Hypoxia also increased the VT:inspiratory time (Ti) ratio, an indicator of central respiratory “drive.” Hypoxia caused consistent, progressive declines in V̇o2, V̇co2, and core temperature (>20% at the lowest SpO2). We propose that optimal quantification of carotid chemoreceptor hypoxic sensitivity in the unanesthetized rodent should employ SpO2[a surrogate for arterial Po2(PaO2)] as the stimulus variable and the ventilatory equivalent for V̇co2(V̇e/V̇co2) and/or mean inspiratory flow rate (VT/Ti) normalized for V̇co2as the response variables. Both metrics take into account not only the important influence of a falling metabolic rate, but also SpO2, which represents the hypoxic stimulus at the carotid body. Because of the somewhat curvilinear nature of these responses, exposure to multiple levels of graded hypoxia provides the most complete characterization of hypoxic chemosensitivity.

Letters to the EditorComments on “Quantifying hypoxia-induced chemoreceptor sensitivity in the awake rodent” by Morgan et al.Vincent JosephVincent JosephCentre de Recherche du CHU de Québec, Hôpital St-François d'Assise, Québec, CanadaPublished Online:15 Dec 2014https://doi.org/10.1152/japplphysiol.00887.2014MoreSectionsPDF (28 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations to the editor: In a recent issue of the Journal of Applied Physiology, Morgan et al. (4) presented a methodological paper for determination of hypoxic ventilatory response in awake rats (4). The method proposes to use the value of the oxygen or carbon dioxide equivalent ratio (V̇e/V̇o2 or V̇e/V̇co2) as a function of SpO2 under graded levels of hypoxia as an accurate way to measure the hypoxic ventilatory response. This approach takes into account the different components of the response to hypoxia, i.e., hyperpnea (increased ventilation) and decreased metabolic rate (V̇o2 and V̇co2) and uses SpO2 as a surrogate for PaO2—the effective stimulus occurring at the level of peripheral chemoreceptors. This approach is a welcome addition to the field and there is no doubt that these parameters must be taken into considerations for adequate and reliable estimation of hypoxic ventilatory response in rodents. We have noticed, however, that the paper proposes few details on the approach used for measurements and calculation of V̇o2 and V̇co2, it is only noted that “Oxygen consumption and carbon dioxide production were measured by sampling O2 and CO2 concentrations in the inspired and expired air.”It is well recognized that measurements of V̇o2 and V̇co2 with this “flow-through” system suffer from three major sources of error: dilution effects of carbon dioxide and water vapor pressure, oxygen analyzer drift, and variability in the CO2 (and H2O) concentration in the inflowing air due the presence of human(s) in the laboratory or to atmospheric conditions (1–3). Furthermore, for the purpose of measurements under hypoxic conditions, an additional source of error that should be considered is the linearity of the O2 analyzers on the range of O2% used, which is particularly important if two different O2 analyzers (or a dual-channel O2 analyzer) are used to measure inflowing and outflowing O2%. Considering the above points, we would like to ask the authors of the abovementioned paper (4) how these potential sources of errors have been taken into consideration for the measurements of V̇o2 and V̇co2?DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).AUTHOR CONTRIBUTIONSAuthor contributions: V.J. drafted manuscript; V.J. edited and revised manuscript; V.J. approved final version of manuscript.REFERENCES1. Jensen DR, Gayles EC, Ammon S, Phillips R, Eckel RH. A self-correcting indirect calorimeter system for the measurement of energy balance in small animals. J Appl Physiol 90: 912–918, 2001.Link | ISI | Google Scholar2. Lighton JR, Halsey LG. Flow-through respirometry applied to chamber systems: pros and cons, hints and tips. Comp Biochem Physiol A Mol Integr Physiol 158: 265–275, 2011.Crossref | ISI | Google Scholar3. Melanson EL, Ingebrigtsen JP, Bergouignan A, Ohkawara K, Kohrt WM, Lighton JR. A new approach for flow-through respirometry measurements in humans. Am J Physiol Regul Integr Comp Physiol 298: R1571–R1579, 2010.Link | ISI | Google Scholar4. Morgan BJ, Adrian R, Bates ML, Dopp JM, Dempsey JA. Quantifying hypoxia-induced chemoreceptor sensitivity in the awake rodent. J Appl Physiol 117: 816–824, 2014.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: V. Joseph, Centre de Recherche du CHU de Québec, Hôpital St-François d'Assise, 10 rue de l'Espinay, Québec, QC, G1L 3L5 (e-mail: Joseph.[email protected]ulaval.ca). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Related ArticlesReply to Joseph 15 Dec 2014Journal of Applied PhysiologyCited ByReply to JosephBarbara J. Morgan, Russell Adrian, Melissa L. Bates, John M. Dopp, and Jerome A. Dempsey15 December 2014 | Journal of Applied Physiology, Vol. 117, No. 12 More from this issue > Volume 117Issue 12December 2014Pages 1524-1524 Copyright & PermissionsCopyright © 2014 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00887.2014PubMed25512068History Published online 15 December 2014 Published in print 15 December 2014 Metrics

BACKGROUND Sildenafil, a selective phosphodiesterase-type-5 (PDE-5) inhibitor, produces vasodilation that improves erectile dysfunction and pulmonary hypertension. Sildenafil could also cause baroreflex sympathetic activation that would enhance vascular tone and oppose direct vasodilation. We tested the hypothesis that sildenafil administration increases sympathetically mediated vascular tone in healthy middle-aged men. METHODS We randomized 9 healthy, middle-aged, male volunteers (mean age 45±2 years) in a double-blind, crossover fashion to receive a single oral dose of sildenafil 100mg or placebo on 2 separate study days. Hemodynamics and forearm blood flow responses were measured at baseline, at 30 and 45 minutes after study drug administration, and then during intra-arterial infusions of vasoactive drugs. After sildenafil and placebo administration, intrabrachial medications were infused to test forearm alpha receptor sensitivity (norepinephrine), cyclic-AMP-mediated vasodilation (isoproterenol), and sympathetically mediated vascular tone (phentolamine) (adenosine was a control vasodilator). Blood samples were taken before and 60 minutes after study drug administration and at the end of the intrabrachial infusions for measurement of plasma norepinephrine concentrations. RESULTS Forearm vascular responses to norepinephrine, isoproterenol, and adenosine were not different after placebo and sildenafil administration. Percentage reduction in forearm vascular resistance during phentolamine was significantly lower after sildenafil than placebo (-73% ± 3% vs -63% ± 3%; P = 0.0002). Sildenafil significantly increased plasma norepinephrine compared with placebo 60 minutes after study drug administration and at the end of the study session (P = 0.02). CONCLUSIONS Sildenafil increased sympathetically mediated vascular tone in middle-aged healthy men. Alpha-adrenergic-mediated vasoconstriction may offset vasodilation during PDE-5 inhibition and may explain the significant hypotension observed in patients taking alpha-blockers with sildenafil.

Background: Xanthine oxidase is a major source of superoxide in the vascular endothelium. Previous work in humans demonstrated improved conduit artery function following xanthine oxidase inhibition in patients with obstructive sleep apnea. Objectives: To determine whether impairments in endothelium-dependent vasodilation produced by exposure to chronic intermittent hypoxia are prevented by in vivo treatment with allopurinol, a xanthine oxidase inhibitor. Methods: Sprague-Dawley rats received allopurinol (65 mg/kg/day) or vehicle via oral gavage. Half of each group was exposed to intermittent hypoxia (FIO2 = 0.10 for 1 min, 15×/h, 12 h/day) and the other half to normoxia. After 14 days, gracilis arteries were isolated, cannulated with micropipettes, and perfused and superfused with physiological salt solution. Diameters were measured before and after exposure to acetylcholine (10–6M) and nitroprusside (10–4M). Results: In vehicle-treated rats, intermittent hypoxia impaired acetylcholine-induced vasodilation compared to normoxia (+4 ± 4 vs. +21 ± 6 µm, p = 0.01). Allopurinol attenuated this impairment (+26 ± 6 vs. +34 ± 9 µm for intermittent hypoxia and normoxia groups treated with allopurinol, p = 0.55). In contrast, nitroprusside-induced vasodilation was similar in all rats (p = 0.43). Neither allopurinol nor intermittent hypoxia affected vessel morphometry or systemic markers of oxidative stress. Urinary uric acid concentrations were reduced in allopurinol- versus vehicle-treated rats (p = 0.02). Conclusions: These data confirm previous findings that exposure to intermittent hypoxia impairs endothelium-dependent vasodilation in skeletal muscle resistance arteries and extend them by demonstrating that this impairment can be prevented with allopurinol. Thus, xanthine oxidase appears to play a key role in mediating intermittent hypoxia-induced vascular dysfunction.