Estimation of alveolar pressure during forced oscillation of the respiratory system.

A method for obtaining a continuous estimate of alveolar pressure (PAlv) during periodic flow is described; it was developed to improve the precision of measurements of airway and respiratory tissue impedance using the improved resolution of relatively high-frequency (approximately 5 Hz) singlas. The respiratory system was modulated with a piston pump, and lung volume and the volume change due to compression and expansion of alveolar gas were measured plethysmorgraphically; these signals and an analog divider were used to obtain a continuous solution of Boyle's law during flow. The plethysmorgraph was of the "flow" type; with it volume changes at frequencies up to 10 Hz and with rates of change up to 6 l/s were measured without amplitude or phase distortion. The method permits control of frequency and flow amplitude during PAlv measurement and calibration of PAlv in the absence of an active chest wall. However, it is technically complex.     

Evaluation of transcutaneous oxygen pressure in adults with respiratory pathology

The usefulness of the transcutaneous oxygen tension (tcPO2) in adults is under controversy. In a varied group of respiratory patients, results of the application of this method were compared with those from the arterial blood sampling method. Thirty-eight arterial oxygen tension (PaO2) and tcPO2 simultaneous determinations were made in a group of 22 patients, while in a sitting position; the tcPO2 measurements obtained (68 +/- 12.36 Torr) were significantly lower (p less than 0.05) than the PaO2 values (74 +/- 13.07 Torr). The correlation coefficient was 0.51 (p less than 0.01) with a regression line, tcPO2 = 31.58 + 0.48 PaO2. It is concluded that tcPO2 measurement does not correlate well with PaO2 and that this method cannot be always be safely applied and used in adults with respiratory diseases.     

Short-term dynamics of relative coordination between respiratory movements, heart rate and arterial pressure fluctuations within the respiratory frequency range

The possible linear short-term coordination between respiratory movements (RESP), heart rate fluctuations (HRF), and arterial blood pressure fluctuations (BPF) in conscious human beings has not yet been investigated because of the restricted time resolution of conventional time series analysis. At present, this short-term dynamics as an expression of relative coordination can be quantified by newly developed adaptive autoregressive modeling of time series using Kalman filtering. Thus, in 6 conscious healthy volunteers, RESP, HRF, and BPF were recorded during 10 min in the supine position, at rest and during paced breathing. A considerable part of calculated ordinary and partial coherence sequences of short-term resolution between RESP and HRF, RESP and BPF, and partially between HRF and BPF showed patterns varying in time that could be correlated to changes between gradual coordinations (coherence changing between 0.40 and 0.95). They were more seldom complete or absent. There were mostly opposite changes between partial coherence sequences RESP-HRF/BPF and RESP-BPF/HRF demonstrating competitive behavior between these coordinations. Paced breathing did not essentially affect any observed characteristics. Therefore, these coherence dynamics are not essentially dependent on voluntary breathing movements. We conclude that to a different extent these linear and changing couplings between RESP, HRF, and BPF in conscious human beings exhibit properties of short-term complete and more frequently gradual coordinations showing dynamics that can not be determined by conventional methods.     

Effects of flooding under hydrostatic pressure on the respiratory metabolism of germinated wheat seeds

Germinated wheat seeds ( Triticum aestivum L. cv. Barqai) that had been subjected to short hydrostatic pressure treatments (0.3–1.2 MPa) changed their normal metabolism into one which is characterized by a high ethanol production, a low O₂ consumption and a low CO₂ evolution. Alcoholic fermentation could account for ca half of the CO₂ evolved from the pressurized seeds. The level of acetaldehyde was low, though significantly higher in the pressurized seeds than in the controls. Subjection of wheat seeds to osmotic stress under aerobic conditions lowered their O₂ uptake and CO₂ evolution but did not induce ethanol production. Exposure of pressurized seeds to NaCl stress did not alter their ethanol production beyond that which had been induced by pressure. Ethanol production by pressurized seeds increased following either the addition of sucrose or by excision of the embryos from the endosperms. More electrolytes leaked into the embedding solution from pressurized seeds than from control seeds. Exogenous ethanol was toxic to wheat seeds at concentrations as low as 343 m M . The effects of hydrostatic pressure and of the consequently induced ethanol production on the mortality of flooded seeds is discussed.     

Effects of changes in CO2 partial pressure on the sensation of respiratory drive

The purpose of this study was to determine whether a change in respiratory sensation accompanies an increase in CO2 partial pressure (PCO2) in the absence of any changes in the level and pattern of thoracic displacement and respiratory muscle force. Eleven normal subjects were artificially hyperventilated with a positive-pressure mechanical respirator. In separate trials the tidal volume (VT) was set at 10 and 18 ml/kg and the frequency of ventilation (f) was adjusted to maintain the base-line end-tidal PCO2 at approximately 30 Torr. Thereafter, at a constant controlled VT and f, the PCO2 was progressively increased by raising the inspired CO2 concentration. There were no changes in respiratory motor activity as determined from the peak inspiratory airway pressure (Paw) until the PCO2 reached 40.8 +/- 1.0 and 40.1 +/- 1.0 (SE) Torr in the large and small VT trials, respectively. Initially there was no conscious awareness of the change in respiratory activity. Subjects first signaled that ventilatory needs were not being satisfied only after a further increase in PCO2 to 44.7 +/- 1.3 and 42.3 +/- 1.0 (SE) Torr in the large and small VT trials and after the Paw had fallen to 55-60% of the base-line value. The results suggest that changes in respiratory sensation produced by increasing chemical drive are a consequence of increases in respiratory efferent activity, but a direct effect of changes in PCO2 on respiratory sensation cannot be excluded.     

Changes in intra-abdominal pressure during postural and respiratory activation of the human diaphragm.

In humans, when the stability of the trunk is challenged in a controlled manner by repetitive movement of a limb, activity of the diaphragm becomes tonic but is also modulated at the frequency of limb movement. In addition, the tonic activity is modulated by respiration. This study investigated the mechanical output of these components of diaphragm activity. Recordings were made of costal diaphragm, abdominal, and erector spinae muscle electromyographic activity; intra-abdominal, intrathoracic, and transdiaphragmatic pressures; and motion of the rib cage, abdomen, and arm. During limb movement the diaphragm and transversus abdominis were tonically active with added phasic modulation at the frequencies of both respiration and limb movement. Activity of the other trunk muscles was not modulated by respiration. Intra-abdominal pressure was increased during the period of limb movement in proportion to the reactive forces from the movement. These results show that coactivation of the diaphragm and abdominal muscles causes a sustained increase in intra-abdominal pressure, whereas inspiration and expiration are controlled by opposing activity of the diaphragm and abdominal muscles to vary the shape of the pressurized abdominal cavity.