Publications (2)7.09 Total impact
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Article: The effects of hypoxia on load compensation during sustained incremental resistive loading in patients with obstructive sleep apnea.
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ABSTRACT: Inspiratory load compensation is impaired in patients with obstructive sleep apnea (OSA), a condition characterized by hypoxia during sleep. We sought to compare the effects of sustained hypoxia on ventilation during inspiratory resistive loading in OSA patients and matched controls. Ten OSA patients and 10 controls received 30 min of isocapnic hypoxia (arterial oxygen saturation 80%) and normoxia in random order. Following the gas period, subjects were administered six incremental 2-min inspiratory resistive loads while breathing room air. Ventilation was measured throughout the loading period. In both patients and controls, there was a significant increase in inspiratory time with increasing load (P = 0.006 and 0.003, respectively), accompanied by a significant fall in peak inspiratory flow (P = 0.006 and P < 0.001, respectively). The result was a significant fall in minute ventilation in both groups with increasing load (P = 0.003 and P < 0.001, respectively). There was no difference between the two groups for these parameters. The only difference between the two groups was a transient increase in tidal volume in controls (P = 0.02) but not in OSA patients (P = 0.57) during loading. Following hypoxia, there was a significant increase in minute ventilation during loading in both groups (P < 0.001). These results suggest that ventilation during incremental resistive loading is preserved in OSA patients and that it appears relatively impervious to the effects of hypoxia.Journal of Applied Physiology 07/2007; 103(1):234-9. · 3.75 Impact Factor -
Article: Cardiac changes during arousals from non-REM sleep in healthy volunteers.
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ABSTRACT: Our aim was to evaluate cardiac changes evoked by spontaneous and sound-induced arousals from sleep. Cardiac responses to spontaneous and auditory-induced arousals were recorded during overnight sleep studies in 28 young healthy subjects (14 males, 14 females) during non-rapid eye movement sleep. Computerized analysis was applied to assess beat-to-beat changes in heart rate, atrio-ventricular conductance, and ventricular repolarization from 30 s before to 60 s after the auditory tone. During both types of arousals, the most consistent change was the increase in the heart rate (in 62% of spontaneous and in 89% of sound-induced arousals). This was accompanied by an increase or no change in PR interval and by a decrease or no change in QT interval. The magnitude of all cardiac changes was significantly higher for tone-induced vs. spontaneous arousals (mean +/- SD for heart rate: +9 +/- 8 vs. +13 +/- 9 beats per min; for PR prolongation: 14 +/- 16 vs. 24 +/- 22 ms; for QT shortening: -12 +/- 6 vs. -20 +/- 9 ms). The prevalence of transient tachycardia and PR prolongation was also significantly higher for tone-induced vs. spontaneous arousals (tachycardia: 85% vs. 57% of arousals, P < 0.001; PR prolongation: 51% vs. 25% of arousals, P < 0.001). All cardiac responses were short-lasting (10-15 s). We conclude that cardiac pacemaker region, conducting system, and ventricular myocardium may be under independent neural control. Prolongation of atrio-ventricular delay may serve to increase ventricular filling during arousal from sleep. Whether prolonged atrio-ventricular conductance associated with increased sympathetic outflow to the ventricular myocardium contributes to arrhythmogenesis during sudden arousal from sleep remains to be evaluated.AJP Regulatory Integrative and Comparative Physiology 03/2007; 292(3):R1320-7. · 3.34 Impact Factor
