Is Silence Really Golden?

Sir,

I have read with great interest the article by Khurana et al on noise(1) and I would like to discuss my observations. Noise is shown to have tremendous impact on physiological responses, including increased heart rate (HR), blood pressure (BP), thyroxine and adrenaline release, dyspnea, anorexia, and insomnia leading to increased complications and prolonged hospitalization. A variety of manifestations such as annoyance, impatience, rage, frustration, uneasiness, insomnia, tachycardia, and easy fatigue may complicate a state that predisposes to hypertension and subsequently to coronary heart disease (CHD), stroke, etc.

Noise stimulates the hypothalamus-pituitary-adrenal gland system to trigger a series of stress hormones and induces a negative magnesium balance resulting in increased peripheral vascular resistance, heart rate, and blood pressure leading to enforced ventricular contractility, hypertension, and subsequent cardiac hypertrophy.(2)

The levels recommended by U.S. Environmental Protection Agency 40-45 dB(A) for day and 35 dB(A) for night] are commonly exceeded. Noise in intensive care units (>60 dB) has been shown to increase heart rate and blood pressure (systolic, diastolic and mean arterial). Noise in neonatal intensive care units (NICUs) has been proposed to impede growth and development in extremely low-birth-weight (ELBW, < 1000 g) newborns. The HR and mean arterial BP significantly correlated with noise in NICU with stronger correlation apparent for higher-birth-weight (probably due to more mature neurological systems).(3)

The night-time noise exposure heightens the hypertension risk compared to daytime because of acute physiologic responses induced by night-time noise events affecting restoration during sleep. The subcortical connections of the auditory pathway with the autonomic nervous system (amygdala, hippocampus, hypothalamus) act in such a way that consciousness is not needed for sound to produce its cardiovascular effects (as evidenced by BP increment when exposed to intense noise even on anaesthesia). Repeated arousals are linked to sustained increase in daytime BP and reinforce the link between acute and long-term effects of noise exposure on hypertension and CHD.(4)

The hypertension and exposure to noise near airports (HYENA) study found statistically significant effects on BP of night-time aircraft noise and average 24-hour road traffic noise exposure. Those sensitive to noise (and with familial hypertension) react with larger increases in vasoconstriction than their “normal” counterparts. A 5 dB increase in measured road traffic noise is associated with 0.8% less dipping in diastolic BP.

A case-control study showed that of the 94% [exposed to > 85 dB (A)] who used hearing protective equipment, 60% sported arterial hypertension compared to the 80% who did not.(5) Children from noisy schools [with higher daytime road-traffic noise Leq>60 dB(A)] are shown to have higher systolic and diastolic pressures compared to those from quiet schools. Also HR was significantly higher (2 beats/min on average) in children from noisy (>45 dB (A) during night) than quiet residences. The Helsinki study showed that occupational exposure to workload or noise with increased blood pressure, glucose or body mass index increases CHD risk.

Noise, now proven to amplify cardiovascular and other morbidities, is a highly underrated risk factor demanding reverberant attention.