Variability of respiratory mechanics during sleep in overweight and obese subjects with and without asthma.

Variability of respiration may provide information regarding disease states. We sought to characterize variability of ventilation and resistance in healthy and asthma, to determine how respiratory control may be altered in sleep and with bi-level positive airway pressure (BPAP). Overweight and obese subjects with and without asthma were studied during sleep at baseline and with BPAP, while measuring respiratory system resistance (Rrs) continuously. Stable periods (>20min) of wake, NREM, and REM sleep were identified and correlation metrics of respiratory parameters were calculated, including coefficient of variation (CV). Variability of Rrs was also characterized over short time scales (20 breaths) during sleep and defined as either "leading to arousal" or "not leading to arousal". Data from 10 control and 10 subjects with asthma were analyzed. CV of Rrs was decreased in asthma at baseline (p<0.001) and decreased on BPAP as compared to baseline (p<0.001). Long time scale correlations were found in respiratory parameters, but the degree of correlations was decreased from wake to sleep (p<0.05). The variance and CV of Rrs was increased preceding an arousal from sleep at baseline; however, during BPAP, the CV was decreased and was not increased preceding arousals. At baseline, resistance was greater in those with asthma, but variability was smaller. BPAP reduced both resistance and overall variability. We conclude that the BPAP-induced decrease in variability may indicate that those with asthma are more likely to remain in a low resistance state, and that low resistance variability may reduce arousals from sleep.

The effect of lung stretch during sleep on airway mechanics in overweight and obese asthma.

Both obesity and sleep reduce lung volume and limit deep breaths, possibly contributing to asthma. We hypothesize that increasing lung volume dynamically during sleep would reduce airway resistance in asthma. Asthma (n=10) and control (n=10) subjects were studied during sleep at baseline and with increased lung volume via bi-level positive airway pressure (BPAP). Using forced oscillations, respiratory system resistance (R(rs)) and reactance (X(rs)) were measured during sleep and R(rs) was partitioned to upper and lower airway resistance (R(up), R(low)) using an epiglottic pressure catheter. R(rs) and R(up) increased with sleep (p<0.01) and X(rs) was decreased in REM (p=0.02) as compared to wake. R(rs), R(up), and R(low), were larger (p<0.01) and X(rs) was decreased (p<0.02) in asthma. On BPAP, R(rs) and R(up) were decreased (p<0.001) and X(rs) increased (p<0.01), but R(low) was unchanged. High R(up) was observed in asthma, which reduced with BPAP. We conclude that the upper airway is a major component of R(rs) and larger lung volume changes may be required to alter R(low).

Phase-rectified signal averaging as a sensitive index of autonomic changes with aging.

Standard heart rate variability (HRV) techniques have been questioned in the sleep and autonomic fields as imprecise measures of sympathetic and parasympathetic activity. A new technique has emerged, known as phase-rectified signal averaging (PRSA). PRSA is used to quantify the quasi-periodic accelerations and decelerations in short-term heart rate, an effect that is normally masked by artifacts and noise. When applied to a signal of peak-to-peak (RR) time intervals, these quasiperiodicities can be used to estimate overall vagal activity, quantified as deceleration capacity (DC) and acceleration capacity (AC). We applied the PRSA analysis to a healthy cohort (ages 21-60 yr) enrolled in a clinical sleep trial, in which ECG data during wakefulness and sleep were available. We found that DC and AC were significantly attenuated with increasing age: a 0.27 ms/yr decrease in DC and a 0.29 ms/yr increase in AC (P<0.001). However, even in the older subjects, DC values were higher then previously found in people post-myocardial infarction. We also found a drop in percentage of normal-to-normal intervals where the current interval deviated>50 ms from the previous interval with age, with a decrease of 0.84%/yr. We did not find any differences between younger and older subjects with traditional HRV techniques, such as low-frequency or high-frequency power. Overall, the study provides normative PRSA data and suggests that PRSA is more sensitive than other HRV measurements. We propose that the decrease in DC and AC may be a sensitive marker for autonomic changes with aging. Further work will be required to determine whether the observed changes predict poorer cardiac health prognosis.

Trace metal concentrations and their distribution in the lobster Panulirus inflatus (Bouvier, 1895) from the Mexican Pacific coast.

The concentration and distribution of Fe, Mn, Ni, Cu, Co, Cd, Cr and Zn among the tissues of female and male lobster Panulirus inflatus from the Pacific coast of México were determined. Distinct inter-tissue and intersize differences in metal concentrations were observed. In general, highest Zn concentrations were found in viscera while highest Cu levels occurred in the gill and gonadal material. The highest Mn, Ni, Cr and Co concentrations were observed in exoskeleton and highest in eggs and gills. Cadmium was undetectable (<0.05 microg g(-1)) in most tissues, only muscle and viscera contained low but detectable amounts. A positive relationship between size and metal concentration was observed only for Zn contained in the muscle of females and males, for Zn contained in the gonad of females, for Mn contained in the gonad of males and for Cu associated with muscle of males. These results are discussed with regard to trace metal concentrations found in temperate and tropical regions.