Aims We tested the hypothesis that body fat percentage determines cardiac sympathovagal balance in healthy subjects. Main methods Heart rate variability (HRV) measurements were made of the standard deviation of the normal– normal RR intervals (SDNN) and the low frequency/high frequency (LF/HF) ratio, from time domain and fast Fourier transform spectral analysis of electrocardiogram RR intervals during trials of uncontrolled and controlled (paced) breathing at 0.2 Hz. Body fat percentage was measured by dual energy x-ray absorptiometric (DEXA) scanning. Significance of differences between uncontrolled and controlled (paced) breathing was determined by analysis of variance and correlations between body fat percentage and HRV measurements by Pearson's coefficient at P<0.05. Key findings Percent body fat was negatively correlated with LF/HF during the uncontrolled breathing (r= −0.56, two-tailed P<0.05, one-tailed P<0.01) but not during the paced breathing trial (r=−0.34, (P>0.1). Significance We conclude that sympathetic activity produced by paced breathing at 0.2 Hz can obscure the relationship between body fat percentage and sympathovagal balance and that high body fat percentage may be associated with low sympathetic modulation of the heart rate in healthy adolescent/young adult males.

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We studied healthy males challenged with a 900 Cal test beverage and correlated EE with the raw (ms2) and normalized units (nu) of total power (TP), low frequency/high frequency (LF/HF) and VLF spectral power of heart rate variability (HRV). The correlations were evaluated during 20 min of normal breathing (NB, control) and 20 min of paced breathing (PB) at 12 breaths·min−1 (0.2 Hz). EE was not significantly correlated with any of the HRV variables before the metabolic challenge. After the challenge, EE was positively correlated with LF/HF and with VLF; VLF was also positively correlated with LF/HF during both NB and PB. These findings suggest that EE may be a correlate of LF/HF and of VLF spectral power of HRV in healthy adolescent/young adult males. The association of lower resting energy expenditure with lower amounts of VLF spectral power may occur in individuals with predilections for obese phenotypes.

S leep disordered breathing (SDB) is a prevalent problem with clinical expression ranging from snoring to severe obstructive sleep apnea (OSA). The OSA syndrome affects at least 5% of the adult population. 1 A growing body of literature attests to significant morbidity associated with even mild OSA. Undiagnosed OSA with or without symptoms has been independently associated with an increased likelihood of systemic hypertension, 2 cardiovascular disease, 3 stroke, and diminished quality of life. 4,5 In addition, there is a well-recognized association between OSA, sleepiness, and automobile accidents in both commercial and noncommercial drivers. 6,7 Severe sleep apnea causes oxygen desaturation, which triggers a catecholamine surge and elevations in blood pressure. 4 This can lead to decompensated congestive heart failure (CHF) and acute stroke in the susceptible indvidiual. 3,4 It has been recognized that the combination of chronic obstructive pulmonary disease and sleep apnea worsens gas-exchange abnormalities during sleep in patients with chronic obstructive pulmonary disease, leading to increased morbidity. 5 In effect, SDB is associated with a myriad of systemic complications.In contrast with the wealth of descriptive information regarding SDB in the outpatient setting, relatively little is known regarding SDB in acutely ill patients. Most studies note the effect of the inpatient setting on sleep quality and quantity. 8 Other studies have described a high frequency of arrhythmias in subjects with SDB. 9 To date, there is no description of the association between SDB and acute exacerbations of cardiopulmonary disease in a large inpatient population. The primary aims of this study are to assess the prevalence of SDB in patients referred for inpatient polysomnography in a tertiary care center and to assess the odds of association of SDB with the underlying acute illness, as well as with patient characteristics. A secondary aim is to evaluate the quality of sleep and type of apneas in the sample. MethodsThe study involved a retrospective chart review of polysomnographic reports and medical records of all patients who had studies done while hospitalized at Johns Hopkins Hospital or Bayview Medical Center between January 2003 and September 2004. Consent for this project was obtained from the Johns Hopkins Institutional Review Board.Total sleep time, sleep stages, sleep efficiency, the presence of SDB, type of apnea, and occurrence of hypoxemia and arrhythmias were noted. Body mass index (BMI) and inpatient