摘要:

The isolated gastrocnemius muscle of the cat was used to study the relation between the desaturation of133xenon measured by external monitoring, and blood flow measured directly by a dropcounter.The metered blood flow agreed with that calculated from the initial slope of the desaturation curve from tissue equilibrated by prolonged intra-arterial infusion and also by atraumatic gas labelling of a local area of the muscle (approximately 0.15% of the muscle weight). In this sense the concept of uniform distribution of blood flow in skeletal muscle has received substantial support. The identity of the results obtained by local gas labelling and by intra-arterial equilibration of the whole muscle with gas implies that there is, at least initially, diffusion equilibrium between tissue and blood in both.However, the clearance curves could in no instance be fitted by a single exponential function. This indicates that the diffusion equilibrium is not maintained after the initial phase. It is suggested that this is not due to the presence of anatomical arteriovenous shunts or other types of uneven perfusion, but to counter current exchange of inert gas through the walls of vessels, i.e. shunting by diffusion explains the shape of the desaturation curves.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

Hemodynamic variability in patients with atrial fibrillation may originate from a direct influence of the variations in RR intervals on myocardial contractility. With the aid of a computer the serial autocorrelation function and the histogram of the RR intervals of patients with atrial fibrillation receiving no medication were produced. The RR intervals were randomly distributed and the histograms rather skew. Next, random rhythms with histograms matching those of the patients were produced with a radioactive source and a Geiger-Müller counter. These rhythms were used to stimulate isolated perfused rat hearts to study the relationship between the RR interval and a number of contractile parameters. The ECG and the isotonic contractions were digitized and processed by the computer. Serial crosscorrelation coefficients were computed between the RR interval on the one hand, and contraction height, contraction area, and maximum of the first derivative of the contraction on the other hand. The zero order crosscorrelation coefficient between the RR interval and contraction height was 0.6, between the RR interval and contraction area 0.8, and between the RR interval and maximum of first derivative 0.5. Although small, the first and second to approximately the tenth order coefficients were definitely negative. It is concluded that during a random rhythm the contractile parameters of an isolated heart are strongly related to the preceding RR interval. It is conceivable that this relation contributes to the variability of hemodynamic parameters during atrial fibrillation in man.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID