A review of heart-rate variability and evaluation

Effect of environmental music on autonomic function in infants in intensive and growing care units

BACKGROUND

The aim of this study is (1) to observe the effect of the background music (BGM) in the incubator on heart rate variability (HRV) during the first few weeks of life in preterm infants in the neonatal intensive (NICU) and growing care units (GCU) and (2) to investigate the effect of environmental music on autonomic function in the infants.

METHODS

Thirty infants, including premature (26 3/7 - 38 4/7 weeks) and low-birth weight (LBW) (946-2,440 g) infants, admitted to the NICU or GCU were involved. The heart rate, low- (LF, 0.05-0.15 Hz) and high- (HF, 0.15-0.4 Hz) frequency HRV components, and LF/HF ratio were measured. The BGM, lullabies for a baby, was delivered through a speaker in the incubator, and the HRV components were compared among before, during, and after intervention with BGM.

RESULTS

The mean HR did not change among the experimental conditions. The LF and HF values decreased during the BGM condition, but not LF/HF, compared with the condition before BGM.

CONCLUSIONS

The present results showed that an auditory environment affected the autonomic function of infants with a range of BGM in the NICU/GCU. The present study also suggested that BGM, a non-invasive and non-pharmacological intervention, could be an evaluation tool for autonomic function in infants in NICU/GCU.

Why is There no Simple Way of Measuring Animal Welfare?

Although the physiological and behavioural changes that can indicate poor welfare are generally agreed upon, using these measures in practice sometimes yields results that are hard to interpret. For example, different types of measure may suggest quite different things about an animal's welfare. Such contradictions are often due to the differing properties of the variables being measured. How each variable responds to a stressor can be affected by several factors - the type of unpleasant stimulus to which the animal is exposed; when and for how long exposure occurs; the animal's psychological state, eg does it feel that it is in control?; and the time at which the measurement is made, relative to the stressor. Typical responses also often differ between species and between individuals, and may even change in a single individual over time. Furthermore, some responses used to assess welfare lack specificity: they can be elicited by neutral or even pleasant events as well as by aversive ones. Appreciating these factors is vital when designing experiments, when choosing what to measure along with each welfare variable, and when interpreting results. Even after taking these factors into consideration, interpreting a result can still be difficult. One approach then is to consider the effects on welfare of the changes measured, eg if there is immunosuppression, does the animal succumb to disease? Another is to use the animal's behaviour to indicate its preference for, or aversion to, particular environments. Ultimately, however, interpreting welfare measures involves subjective judgements which will be influenced by the nature of our concern for the animal under consideration. By raising these problems, we hope that this review will highlight and clarify the apparent contradictions that sometimes emerge in scientific studies of animal welfare, and help researchers improve the designs of their experiments for the benefit of the animals concerned.

Cardiovascular variability and introversion/extroversion, neuroticism and psychoticism

Forty-eight subjects were measured during a 10 min rest period for pulse wave velocity (PWV) and heart rate (HR) level and variability, using a Cyborg BL 907 instrument. These subjects were also evaluated by means of the Eysenck Personality Questionnaire for I-E, N, P and L. These data were factor analyzed. Five factors were identified which were accounted for 80.6% of the variance. These factors were: 'cardiovascular lability', 'heart rate time trends', 'cardiovascular balance', 'sex effects' and 'self reports'. The EPQ measurements separated from the physiological measurements in the factor analysis and none were found to be significantly loaded on any physiological variables. On the other hand, significant physiological correlations were found with N. This study adds a possible blood pressure and heart rate descripter to N.