Reproducibility of the heart rate variability responses to graded lower body negative pressure

Abstract

The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or -100 mmHg, separated by 1 week. Heart rate, stroke volume (impedance cardiography), blood pressure (Finapres), and forearm blood flow were assessed, as was HRV in both time and frequency domains. The trial-to-trial responses to LBNP common to all subjects (LBNP< or =-60 mmHg and at test termination) showed parallel changes, suggesting similar responses between both trials. Good reproducibility estimates were found for the resting HRV data (lowest: R=0.62 for low frequency/high frequency ratio; highest: R=0.94 for standard deviation of normal R-R intervals). During LBNP, reproducibility estimates varied but were generally similar to that seen at rest. At test termination, they were unacceptably low (R<0.41) for the HRV data assessed in the frequency domain and expressed in absolute units. LBNP tolerance was lower in the first trial [LBNP tolerance index: 404 (21) versus 437 (15) mmHg min(-1); P<0.05] but the intraclass correlation coefficient was high (R=0.87). These data suggest that (1) HRV responses to submaximal LBNP up to -60 mmHg are consistent across trials, (2) the considerable variability seen in the HRV parameters at maximal LBNP can be reduced by expressing these data in either the time domain or using normalized units in the frequency domain, and (3) cardiovascular responses to sub- and maximal LBNP are reproducible. Data are presented as mean (SEM) unless otherwise stated.

Reliability and accuracy of heart rate variability metrics versus ECG segment duration

“…Some studies concluded that their examined HRV metrics were reliable [2,5,8,13,14,18,19,25,29,31,34,35,39,41,50,55,58,59,60,61], while others found the reliability to be moderate or low [6,23,33,51,56,62]. This discrepancy of results may be due, in part, to the fact that these studies examined distinct subject populations, and their conclusions on HRV reliability apply only to the specific HRV metrics studied.…”

“…In general, the objective of previous works has been to assess the reproducibility of a subset of the HRV metrics used to study a specific patient population or condition of interest. These studies include research on the shortand long-term reproducibility of autonomic measures in supine and standing positions [31], reproducibility of HRV responses to graded lower body negative pressure [20,34], reliability of short-term HRV measures during exercise [3,28,30,62], reproducibility of measures of cardiovascular autonomic nervous function in middle age and elderly subjects [23], reproducibility of frequency domain HRV metrics before and after a standardized meal [18], HRV analysis reproducibility in the chronic phase of myocardial infarction [5], reproducibility of HRV from short-term recording during manoeuvres in normal subjects [9], stability of short recordings in time [54] and reproducibility of HRV metrics obtained from short-term sampling records [21,37]. In addition to the reproducibility of 24 h and 5 min records, assessing the reproducibility of HRV metrics calculated from very short records has significant practical importance [25], since it is not always possible to obtain 5 min records due to instrumentation constraints or study design [17].…”

Reactive hyperemia in the human liver

“…Finapres measurements correlate well with intra-arterial measurements of blood pressure (22) and have been validated in subjects undergoing stress situations (30). Hemodynamic monitoring with the Finapres system has its own limitations since it may be affected by bias and drift and, therefore, relative changes in blood pressure were analyzed rather than absolute values (26). To avoid any drift, we calibrated to absolute values from conventional cuff measurements on the contralateral upper arm every 15 min.…”

Error and Individual Difference in Cardiovascular Responses to Orthostatic Stress in Humans

“…Nevertheless, if there were only single measurements in each subject, the results then would be ambiguous. Lee et al (2004) have reported the use of high reproducible responses between two trials of cardiovascular regulation in grading lower body negative pressures; however, there were significantly higher sympathetic activations at the first compared with the second trial. Although we prepared the subjects in the preliminary session to accommodate the experimental protocol, high percentages of day-to-day differences in HR during supine rest condition were noted.…”

“…Numerous studies have investigated the reproducibility of cardiovascular responses to the postural effect in clinical populations (Vardas et al, 1994;Ward and Kenny, 1996), normal young (Lee et al, 2004;Cloarec-Blanchard et al, 1997) and healthy elderly subjects (Mehagnoul-Schipper et al, 2001). Although these studies mentioned reproducibility within the same subject, the variations between the subjects were omitted in their data analyses using statistical correlations or changes in value from the supine baseline.…”