Cardiovascular autonomic modulation during 36 h of total sleep deprivation (SD) was assessed in 18 normal subjects (16 men, 2 women, 26.0 +/- 4.6 yr old). ECG and continuous blood pressure (BP) from radial artery tonometry were obtained at 2100 on the first study night (baseline) and every subsequent 12 h of SD. Each measurement period included resting supine, seated, and seated performing computerized tasks and measured vigilance and executive function. Subjects were not supine in the periods between measurements. Spectral analysis of heart rate variability (HRV) and BP variability (BPV) was computed for cardiac parasympathetic modulation [high-frequency power (HF)], sympathetic modulation [low-frequency power (LF)], sympathovagal balance (LF/HF power of R-R variability), and BPV sympathetic modulation (at LF). All spectral data were expressed in normalized units [(total power of the components/total power-very LF) x 100]. Spontaneous baroreflex sensitivity (BRS), based on systolic BP and pulse interval powers, was also measured. Supine and sitting, BPV LF was significantly increased from baseline at 12, 24, and 36 h of SD. Sitting, HRV LF was increased at 12 and 24 h of SD, HRV HF was decreased at 12 h SD, and HRV LF/HF power of R-R variability was increased at 12 h of SD. BRS was decreased at 24 h of SD supine and seated. During the simple reaction time task (vigilance testing), the significantly increased sympathetic and decreased parasympathetic cardiac modulation and BRS extended through 36 h of SD. In summary, acute SD was associated with increased sympathetic and decreased parasympathetic cardiovascular modulation and decreased BRS, most consistently in the seated position and during simple reaction-time testing.

Wadhwa H, Gradinaru C, Gates GJ, Badr MS, Mateika JH. Impact of intermittent hypoxia on long-term facilitation of minute ventilation and heart rate variability in men and women: do sex differences exist? J Appl Physiol 104: 1625-1633, 2008. First published April 10, 2008 doi:10.1152/japplphysiol.01273.2007.-Following exposure to intermittent hypoxia, respiratory motor activity and sympathetic nervous system activity may persist above baseline levels for over an hour. The present investigation was designed to determine whether sustained increases in minute ventilation and sympathovagal (S/V) balance, in addition to sustained depression of parasympathetic nervous system activity (PNSA), were greater in men compared with women following exposure to intermittent hypoxia. Fifteen healthy men and women matched for age, race, and body mass index were exposed to eight 4-min episodes of hypoxia during sustained hypercapnia followed by a 15-min end-recovery period. The magnitude of the increase in minute ventilation during the endrecovery period, compared with baseline, was similar in men and women (men, 1.52 Ϯ 0.03; women, 1.57 Ϯ 0.02 fraction of baseline; P Ͻ 0.0001). In contrast, depression of PNSA and increases in S/V balance were evident during the end-recovery period, compared with baseline, in men (PNSA, 0.66 Ϯ 0.06 fraction of baseline, P Ͻ 0.0001; S/V balance, 2.8 Ϯ 0.7 fraction of baseline, P Ͻ 0.03) but not in women (PNSA, 1.27 Ϯ 0.19 fraction of baseline, P ϭ 0.3; S/V balance, 1.8 Ϯ 0.6 fraction of baseline, P ϭ 0.2). We conclude that a sustained increase in minute ventilation, which is indicative of longterm facilitation, is evident in both men and women following exposure to intermittent hypoxia and that this response is independent of sex. In contrast, sustained alterations in autonomic nervous system activity were evident in men but not in women. carbon dioxide; parasympathetic nervous system; sympathovagal balance LONG-TERM FACILITATION (LTF) of minute ventilation and/or its components (i.e., tidal volume and breathing frequency) may be elicited during and following short-term exposure to intermittent hypoxia (i.e., 20 -30 min) (38,40,44). LTF is characterized by a gradual increase in respiratory motor activity during successive periods of normoxia that separate hypoxic episodes and by respiratory activity that remains elevated for up to 90 min following exposure to intermittent hypoxia (40). LTF of minute ventilation or phrenic nerve activity (3,10,22,48,49) and genioglossus muscle or hypoglossal nerve activity (2, 18, 34, 37) have been observed in goats (49), dogs (10), cats (34), ducks (41), rats (3, 18), and mice (48). Similarly, LTF of minute ventilation and genioglossus muscle activity have been observed in healthy humans (21) during wakefulness when carbon dioxide levels are sustained slightly above baseline values during and following exposure to intermittent hypoxia. However, LTF is absent in healthy individuals (14,24,35,36,43) and individuals with obstructive sleep apnea (26) when carbon dioxid...

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