Reliability and validity of measures of cardiac output during incremental to maximal aerobic exercise - Part I: Conventional techniques

The assessment of cardiac function, particularly cardiac output (Q) during heavy exercise is essential for the evaluation of cardiovascular factors th at might limit oxygen transport. A series of invasive and noninvasive techn iques has been developed for the assessment and monitoring of if during res ting and submaximal exercise conditions. However, very few techniques have been found to give accurate and reliable determinations of (Q) over dot dur ing Vigorous to maximum exercise. For exercise physiologists and sport card iologists, maximal exercise data are of primary importance. The 'gold standard' measures of cardiac function are considered to be the d irect Fick and dye-dilution methods. These have been widely shown to give a ccurate and reliable determinations of (Q) over dot during resting and subm aximal exercise conditions; however, their use during maximal exercise cond itions is debatable due to the inherent risks involved with each and their increasing inaccuracy during the later stages of vigorous exercise. Thermod ilution has also been considered to be a relatively good method for the det ermination of (Q) over dot during rest and exercise conditions, but recent authors have questioned its use due to the nature of the measure and its in accuracy during strenuous exercise. Various noninvasive measures of cardiac function have been developed to ove rcome the problems associated with the 'gold standard' measures. The first part of this article discusses conventional techniques used in exercise phy siology settings. The majority of these provide accurate and reliable deter minations of (Q) over dot during rest and submaximal exercise. However, ver y few techniques are suitable for maximal exercise conditions. Perhaps only the foreign gas rebreathe using acetylene (C2H2) meets all the criteria of being noninvasive, simple to use, reliable over repeated measurements, acc urate and useful during maximal exercise.