HEART RATE AND BLOOD PRESSURE

Heart Rate and Blood Pressure



Heart Rate and Blood Pressure

Introduction

Cardiac failure and ischaemic heart disease patients receive standard of care cardiac b1-adrenergic blockade medication. Such medication reduces cardiac output and cerebral blood flow. (Ainslie 2005)

Material and methods

Eight healthy non-athletic men, age 22 - 2 years, height 181 - 10 cm, weight 71 - 9 kg (mean - SD) were recruited to participate in the study as approved by the Ethics Committee of Copenhagen (KF 01-369/ 97). All subjects were not performing endurance training on a regular basis. In addition, they were free of any known cardiovascular and pulmonary disorders and were not using prescribed or over the counter medications. Before the experiment, each subject gave informed written consent and visited the laboratory for familiarization with the techniques and procedures.

Subjects were requested to abstain from caffeinated beverages for 12 h and strenuous physical activity and alcohol for at least 24 h before the day of the experiment.

Measurements

A catheter (1.1 mm ID, 20 gauge) was placed in the brachial artery of the non-dominant arm for measurement of the arterial pressure with a Bentley transducer (Uden, the Netherlands) positioned at the level of the right atrium in the mid-axillary line, fastened to the subject and connected to a pressure monitoring system (Danica, Copenhagen, Denmark). Beat-to-beat data of cardiovascular variables were collected on a personal computer with customized data acquisition software.

The HR, MAP, stroke volume and thus cardiac output were calculated from the blood pressure waveform using the Modelflow software program that is incorporated in the beatscope version 1.0 software incorporating age, sex, height and weight (TNO-TPD; Biomedical Instrumentation, Amsterdam, the Netherlands).

Arterial blood samples were obtained at rest and after reaching steady-state in each exercise bout. Samples were immediately analysed for PaCO2 and blood lactate concentration (ABL725; Radiometer, Copenhagen, Denmark). The MCA Vmean was obtained by transcranial Doppler ultrasonography (Multidop X; DWL, Sipplingen, Germany). A 2-MHz Doppler probe was placed over the temporal window and fixed with an adjustable headband and adhesive ultrasonic gel (Tensive; Parker Laboratories, Orange, NJ, USA). The MCA V waveform was isonated at the same depth (5 cm from the skin surface of the temple window) in all subjects. (Ainslie 2005)

Data analysis

Analogue signals of blood pressure and the spectral envelope of MCA Vmean were sampled at 100 Hz and digitized at 12 bits for off-line data analysis. Beat-tobeat cardiac output, MAP, HR and MCA Vmean were obtained by integrating analogue signals within each cardiac cycle. The beat-to-beat data of cardiac output, MAP, HR and MCA Vmean were then linearly interpolated and re-sampled at 2 Hz for spectral analysis. The transfer gain and phase shift reflect the relative amplitude and time relationship between the changes in two variables (cardiac output or MAP and MCA Vmean, or HR and MAP) over a specified frequency range. From the temporal sequences, the frequency-domain transforms are computed with a fast Fourier transformation algorithm. The transfer function H (f ) between the two signals was calculated as H (f ) ¼ Sxy (f ...