Haemodynamics during sleep: old results and new perspectives

After the advent of polygraphic recordings in the 1960s a great deal of interest focused on cardiocirculatory and respiratory activity during sleep. The Bologna sleep laboratory was the first to make direct recordings of systemic arterial pressure, pulmonary arterial pressure and alveolar ventilation in normal subjects, measuring gas-blood values during different sleep stages. In the 1960s, neurophysiologists rediscovered a syndrome known to pneumologists for a decade as Pickwickian Syndrome. Polygraphic studies performed in sleep laboratoires all over Europe (Germany, France and Italy) led to a major discovery: the syndrome was not caused by respiratory overload due to obesity, but usually by the presence of obstructive apnoeas arising during sleep. By means of continuous sleep recordings, our laboratory documented the severe repercussions of apnoeas on ventilatory and cardiocirculatory functions. Hypnologists pointed to tracheostomy as the logical effective treatment for the syndrome. Surgery was first performed in Germany by Kuhlo and coworkers and then in Bologna. In the early 1970s, following the Bologna group's research, there emerged the now accepted concept that obstruction of the upper airways is a continuum stretching from snoring to full-blown sleep apnoea syndrome. The Bologna team was also the first to conduct epidemiological surveys that indicated that snoring is a relevant risk factor for the cardiocirculatory system. Here the trends of haemodynamic and ventilatory parameters during sleep are investigated in syndromes of obstructive respiratory failure. The conclusion is that sleep, particularly REM-sleep, exacerbates all these disorders, and the topic provides a basis for a wider look at how cardiocirculatory activity varies during sleep under normal and pathological conditions.