. Heart rate variability and spontaneous baroreflex sequences in supine healthy volunteers subjected to nasal positive airway pressure. J Appl Physiol 99: [2137][2138][2139][2140][2141][2142][2143] 2005. First published July 7, 2005; doi:10.1152/japplphysiol.00003.2005.-To determine the dynamic effects of short-term nasal positive airway pressure (nPAP) on cardiovascular autonomic control, continuous recordings of noninvasively obtained hemodynamic measurements and heart rate variability (HRV) were obtained in 10 healthy subjects during frequency-controlled breathing (between 0.20 and 0.24 Hz) in supine posture under different pressures of nPAP ranging from 3 to 20 cmH 2O. HRV was assessed using spectral analysis of the R-R interval. The slope of the regression line between spontaneous systolic blood pressure and pulse interval changes was taken as an index of the sensitivity of arterial baroreflex modulation of heart rate (sequence method). Application of nPAP resulted in a pressure-dependent decrease of cardiac output and stroke volume (P Ͻ 0.05, ANOVA) and in an increase in total peripheral resistance (P Ͻ 0.03, ANOVA). Hemodynamic changes under increasing nPAP were accompanied by a decrease in total power of HRV despite mean R-R interval remaining unchanged. The overall decrease in HRV was accompanied by a reduction across all frequency bands when absolute units were used (P Ͻ 0.01). When the power of low frequency and high frequency was calculated in normalized units, a diminished high frequency and an increased low-to-high frequency ratio were observed (P Ͻ 0.05). Compared with low levels of nPAP, pressure levels of Ͼ10 cmH 2O were associated with a significant decline in the mean slope of spontaneous baroreceptor sequences (P Ͻ 0.04). These findings indicate that short-term administration of nPAP in normal subjects exerts significant alterations in R-R interval variability and spontaneous baroreflex modulation of heart rate. cardiac output; cardiovascular autonomic control; heart-lung interaction RESPIRATION SIGNIFICANTLY INFLUENCES autonomic cardiovascular control (12). During normal breathing, oscillatory changes of left ventricular stroke volume (SV) and arterial blood pressure (BP) are sensed by baroreceptors, which provoke parallel R-R interval changes by means of baroreflex physiology (27). Hemodynamic oscillations during normal (negative pressure) respiration are predominantly due to changes in intrathoracic pressure (ITP) (30). However, little is known about the effects of augmented positive ITP, which occurs with positive airway pressure (PAP) ventilation, on cardiovascular autonomic control. The application of PAP, both invasively or noninvasively, increases ITP and may result in a reduction in cardiac filling pressures (23,29,37,43). A reduction in cardiac filling pressures associated with PAP (or positive end-expiratory pressure) may induce a compensatory increase in vascular resistance to maintain systemic arterial pressure in the face of a reduced cardiac output (CO) (5, 41). The increase in...

The paper deals with the classical two‐sample testing problem for the equality of two populations, one of the most fundamental problems in biomedical experiments and case–control studies. The most familiar alternatives are the difference in location parameters or the difference in scale parameters or in both the parameters of the population density. All the tests designed for classical location or scale or location–scale alternatives assume that there is no change in the shape of the distribution. Some authors also consider the Lehmann‐type alternative that addresses the change in shape. Two‐sample tests under Lehmann alternative assume that the location and scale parameters are invariant. In real life, when a shift in the distribution occurs, one or more of the location, scale, and shape parameters may change simultaneously. We refer to change of one or more of the three parameters as a versatile alternative. Noting the dearth of literature for the equality two populations against such versatile alternative, we introduce two distribution‐free tests based on the Euclidean and Mahalanobis distance. We obtain the asymptotic distributions of the two test statistics and study asymptotic power. We also discuss approximating p‐values of the proposed tests in real applications with small samples. We compare the power performance of the two tests with several popular existing distribution‐free tests against various fixed alternatives using Monte Carlo. We provide two illustrations based on biomedical experiments. Unlike existing tests which are suitable only in certain situations, proposed tests offer very good power in almost all types of shifts.

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The c-sample location problem with umbrella alternatives is investigated. The umbrella peak l is assumed to be unknown. All test statistics are maxima of substatistics which are constructed for the case of a known peak l. These substatistics are based on ranks. Arbitrary scores and arbitrary sample size configurations are allowed. As special cases we have tests of Chen and Wolfe [Chen, Y.I. and Wolfe, D.A., 1990, A study of distribution-free tests for umbrella alternatives. .]. We compute the asymptotic power functions of the constructed tests.For the cases of three or four treatments, some figures give an impression of the asymptotic power functions for various setups. Simulation studies show that the asymptotic results can also be used for moderate sample sizes. In average, over all setups, the Hettmansperger-Norton-type test performs best densely followed by the Chen-Wolfe-type test and the Shi-type test.

For the c-sample location problem with ordered alternatives we compare a test proposed by Barlow et al. (1972) and its Welch modification for the case of unequal variances with some nonparametric counterparts, the Jonckheere test and modifications of the Jonckheere test. In these modifications the Mann-Whitney statistic is replaced by other two-sample linear rank statistics. The comparison is referred to the actual level and the power of the tests and it is carried out via Monte Carlo simulation assuming short-, medium-and long-tailed as well as asymmetric distributions. It turns out that in the case of unequal variances and symmetric distributions the Welch modification of the test of Barlow et al. is the most I-robust test among the tests considered, but for equal variances special Jonckheere-type tests are to be preferred.

Background: In recent studies, the efficacy of intermittent rest of the inspiratory muscles as an option of treating patients with severe chronic obstructive pulmonary disease (COPD) has become questionable. Objective: The aim of our study was to analyze the effects of feedback-controlled intermittent negative pressure ventilation (INPV) on stable, but severely hypercapnic COPD patients. Methods: 21 clinically stable, hypercapnic patients with severe COPD underwent INPV with chest shells for 3 weeks, 6 h a day. The INPV sessions were optimized by a visual biofeedback system, which enabled control over the decrease in diaphragmatic activity. Respiratory muscle (RM) function parameters, lung function parameters, blood gases and exercise capacity were analyzed. Results: In the end, 19 patients concluded INPV treatment. They had PaO₂ of 56.5 ± 11.8 mm Hg, PaCO₂ of 50.2±2.7 mm Hg (mean ± SD) and FEV₁ of 27.8 ± 4.3% predicted before treatment. There was no statistically significant change in lung function parameters, RM function parameters, physical performance and level of dyspnea after 3 weeks of INPV. Conclusion: We conclude that intermittent RM rest induced by INPV can relax inspiratory muscles in most patients with stable severe COPD, but fails to improve RM function and exercise capacity.

For the c-sample location problem with ordered alternatives, the test proposed by Barlow et al. (1972 p. 184) is an appropriate one under the model of normality. For non-normal data, however, there are rank tests which have higher power than the test of Barlow et al., e.g. the Jonckheere test or so-called Jonckheere-type tests recently introduced and studied by Büning & Kössler (1996). In this paper the asymptotic power of the Jonckheere-type tests is computed by using results of Hájek (1968) which may be considered as extensions of the theorem of Chernoff & Savage (1958). Power studies via Monte Carlo simulation show that the asymptotic power values provide a good approximation to the finite ones even for moderate sample sizes.