Search PubMed⌕ Search

Biomedical subjects

H Worth

Publications and source records attributed to H Worth.

122 records · Page 7Linked to original sources
PubMed1977

Respiration and circulation during swimming activity in the dogfish Scyliorhinus stellaris.

A number of respiratory and circulatory parameters was measured in the Larger Spotted Dogfish Scyliorhinus stellaris before, during and after periods of spontaneous swimming. During swimming the gill ventilation was increased, mainly due to increased ventilatory stroke volume, the respiratory frequency showing a small rise only, and the cardiac output was increased at only slightly elevated cardiac frequency. Coordination between cardiac, ventilatory or locomotor (tail-beat) rhythms was not observed. The decrease in utilization of inspired water O2 during swimming was attributable to diffusion limitation in branchial O2 transfer. A considerable fraction of the total net amount of O2 required for swimming was taken up during the recovery phase. From the observations that (1) the decrease in gill ventilatory flow after cessation of swimming revealed a very rapid component (followed by a slow component), and that (2) changes in swimming speed were reflected by immediate changes in momentary ventilatory flow, it is concluded that the increased ventilation during swimming was in part mechanical-passive and/or due to nervous coupling between respiratory and locomotor centers.

Animals↗
PubMed1977

Penetration of inhaled He and SF6 into alveolar space at low tidal volumes.

To study mixing of inspired gas with lung gas, penetration of simultaneously inspired helium (He) and sulfur hexafluoride (SF6) into alveolar space was determined in normal subjects at low tidal volumes (from 50 to 500 ml) and at varied lung volumes and speeds of inspiration/expiration. The volume of inspired gas reaching the alveolar space, termed alveolar-tidal volume, VTA, was calculated from preinspiratory lung volume, inspired volume, and inspired and expired alveolar test gas concentrations. The difference between the VTA values calculated for He and SF6, VTA(He) - VTA(SF6), was influenced by tidal volume, lung volume, and the speed of inspiration/expiration, but it was always positive. The results are qualitatively explainable on the basis of easier diffusive mixing of He in lung airways compared with SF6. Since Taylor dispersion would produce deeper penetration, and therefore higher VTA, for a less diffusible gas the results provide no evidence for its implication in pulmonary gas exchange.

Adult↗
PubMed1976

Pulmonary gas exchange in dogs ventilated with mixtures of oxygen with various inert gases.

To study the influence of physical properties of the respired gas on alveolar gas exchange, alveolar-arterial partial pressure differences for O2 and CO2 were measured in anesthetized dogs that were artificially ventilated with gas mixtures of O2 in N2, He, Ar or SF6. In both hyposia and normoxia alveolar-arterial PO2 differences had the tendency to increase slightly in the sequence of the respired inert gases SF6 less than Ar less than N2 less than He, while arterial-alveolar PCO2 differences remained practically unchanged. Pulmonary diffusing capacity for CO(DCO), determined by the single breath technique, revealed no significant differences between the four gas mixtures used. The possible mechanisms underlying these results are discussed in connection with the physical properties of the respired gas mixtures.

Animals↗
PubMed1976

Gas-blood CO2 equilibration in parabronchial lungs of birds.

We have conducted two experimental series in the chicken in order to study CO2 exchange in the parabronchial lungs of birds. In the first series, the animals were artifically ventilated and end-expired PCO2, PE'CO2, was measured and compared with mixed venous PCO2, PVCO2. On the average, PECO2 exceeded PVCO2 by 2.8 Torr. In the second series, rebreathing was used to investigate the mechanism of this positive (PE'-PV)CO2 difference. Lung gas PCO2 was found to equilibrate with PVCO2 if both CO2 and O2 exchange in the lung was abolished during rebreathing. Only if O2 uptake continued, we observed a positive gas-to-mixed venous blood PCO2 difference. The results suggest that positive gas-blood PCO2 differences both during rebreathing and steady-state ventilation are brought about by the Haldane effect. Model calculations show that in the homogeneous avian lung, unlike in the alveolar lung, the Haldane effect can produce positive (PE'-PV)CO2 differences during steady-state breathing due to the peculiarities of the crosscurrent arrangement and parabronchial ventilation and blood perfusion.

Animals↗
PubMed1975

[Pulmonary diffusing capacity for CO during breathing of inert gas mixtures with differing physical properties (author's transl)].

In order to study the role of diffusion limitation in alveolar space (stratification) for pulmonary gas exchange function, pulmonary diffusing capacity for CO (Dco) was comparatively measured during breathing of room air and of gas mixtures in which N2 of room air was replaced by He or Ar. Measurements in 15 healthy humans using the single breath method yielded the following mean (+/-SE) values: room air, 22.1+/-1.7; He, 25.1+/-1.3; Ar, 17.4+/-1.0 ml-min-1-Torr-1. The clear negative correlation between Dco and the molecular weight of the gases used is most easily explained on the basis of an airway diffusion resistance limiting CO transfer. For room air breathing this resistance is estimated at about 10% of the total resistance to CO uptake (1/Dco). The alveolar exchange of O2 and CO2 is expected to be affected by the diffusional resistance in airways, particularly at high metabolic levels.

Adolescent↗
PubMedDate not supplied

Cournand lecture. Expiratory partial pressure curves in the diagnosis of emphysema.

The deformation of expiratory partial pressure curves of respiratory and inert gases (O2, CO2, He, Ar, SF6), as measured by means of mass spectrometry, was analysed in healthy subjects and in patients with asthma, chronic bronchitis and/or pulmonary emphysema. Patients with emphysema could best be distinguished from the other groups when the comparison was based on the shape of expirogram phase II. Phase II was characterized by the volume V25-50 which was expired between 25% and 50% of the inspiratory/end-tidal partial pressure difference. Comparative measurements of V25-50 of O2, CO2, He and SF6 in 10 healthy subjects (mean age: 30.8 yr) and in 10 patients with advanced emphysema (mean age: 60.8 yr) showed a linear increase of V25-50 with increasing inspired volume (VI) being 3-5 times higher in the patients than in normals. V25-50 increased with the sequence He less than SF6 approximately equal to CO2 less than O2 in both groups. The separation between phase II volumes of He and SF6 was more pronounced in the patients with emphysema than in the healthy subjects. Variations of the breathing pattern in eight healthy subjects revealed a linear increase of V25-50 with increasing VI and, to a lower extent, with increasing respiratory frequency, while a decrease of V25-50 with increasing breath-holding time and only very small changes with variations of inspiratory as well as expiratory duration were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMedDate not supplied

[Analysis of myocardial evoked potentials in relation to ergometric load and heart rate for use in frequency-adaptive cardiac pacemakers].

The aim of this study was to evaluate the ventricular evoked response (VER) measured with unipolar fractally coated pacing leads for use with rate-responsive pacemakers. To this end, the morphology of the VER, its variation with pacing rate and various levels of physical loading, and the long-term stability of the signal were studied using the telemetric features of implantable pacemakers. Fractally coated electrodes were used in order to minimize the stimulation artefact, thus enabling a reliable unipolar measurement of the VER. The VER shows uniform basic morphology, and remains virtually unchanged after 3 months; moreover, frequency and load-dependent changes of VER morphology were identical for all patients. A special programming device has been developed to evaluate a rate adaptive algorithm for optimizing the pacing rate to the current loading situation, and was successfully tested in two patients. The algorithm was shown to be capable of calculating a heart rate adequate for haemodynamic demand.

Aged↗