Subramani, S. | bioRxiv Science

bioRxiv2019

Phenylephrine induces relaxation of longitudinal strips from small arteries of goat legs

Alpha adrenergic stimulation is known to produce vasoconstriction. We have earlier shown that, in spiral strips of small arteries Phenylephrine (PE) caused vasorelaxation under high nitric oxide (NO) environment. However on further experimentation it was realized that the PE-induced vasorelaxant response occurred only with longitudinal strips of small arteries even under normal NO environment while circular strips showed contraction with PE even under high NO environment. Such PE-induced vasorelaxation of longitudinal strips was blocked by Phentolamine, an alpha-adrenergic receptor blocker. On delineation of specific receptor subtype, PE-induced relaxation was found to be mediated through alpha 1D receptor. However, this phenomenon is specific to small artery, as longitudinal smooth muscle of aorta showed only contractile response to adrenergic stimulation. There is no prior report of longitudinal smooth muscle in small artery up to our knowledge. The results of this study and histological examination of vessel sections suggest the presence of longitudinal smooth muscle in small artery and their relaxant response to alpha adrenergic stimulation is a novel phenomenon.

physiology↗

bioRxiv2019

Blood pressure variability from intra-arterial recordings in humans

Systolic and diastolic blood pressures are reported as single point values by the non-invasive techniques used in clinical practice, while, in fact, they are highly varying signals. The objective of this study was to document the magnitude of variation of systolic and diastolic pressures over a few minutes by analysing intra-arterial pressure recordings made in 51 haemodynamically stable patients in an intensive care unit. Intra-arterial pressure data were acquired by a validated data acquisition system. Fast-Flush test was performed and the dynamic characteristics of the catheter transducer system namely natural frequency and damping co-efficient were calculated. Only those recordings with acceptable dynamic characteristics were included in the analysis. Power spectral calculation using the Discrete Fourier transform (DFT) of the pressure recording revealed two frequency peaks below the peak at heart rate. The lower and higher frequency peaks below the heart rate peak are referred to as Mayer and Traube waves in this study. Mayer wave peaks were observed in DFT spectra of 49 out of 51 patients. The Mayer wave frequency peaks ranged between 0.045 Hz to 0.065 Hz in 41 out of 51 patients. The frequency of Traube waves or the respiratory variations was more than 0.14 Hz. Three categories of systolic and diastolic pressure variabilities namely beat-to-beat variability, Respiratory variability (Traube wave amplitude) and Total magnitude of variation are reported for all 51 patients. The mean systolic and diastolic pressure variations (in a period of about 10 minutes) in the study sample were 21 {+/-} 9 mm Hg and 14 {+/-} 5 mm Hg respectively. Given the magnitude of systolic and diastolic pressure variations over a few minutes, the validity of reporting single point values for these pressures and using single point cut-offs for diagnosis and treatment of hypertension must be re-evaluated.

physiology↗