Historical Background and Glossary of the Apnea Phenomenon

Abstract

Periodic breathing (PB) or Cheyne-Stokes respiration (CSR) is an oscillatory breathing pattern characterized by hypopneas (in PB) or apneas (in CSR) of central origin, alternated to hyperventilation. After the reports by Hippocrates and an eighteenth-century surgeon, PB/CSR was extensively described in the nineteenth century in patients with end-stage heart failure (HF). In the following decades, PB/CSR was characterized as a phenomenon manifesting in healthy people after hyperventilation or at high altitudes but also occurring in different conditions whose common denominator is a functional impairment of the respiratory centers. With the development of sleep medicine, the attention shifted on obstructive apneas. A new interest for PB/CSR rose in the 1990s, when researches in the setting of HF progressively disclosed the mechanisms of PB/CSR, evaluated its prognostic value, and the therapeutic option.

In the present chapter, a historical background and a brief glossary will introduce the reader to the following chapters, dealing with the state of the art of research about PB/CSR in HF.

Appendix: A Brief Dictionary of Breathlessness

Herein, the current definitions of the main terms pertaining to PB/CSR will be provided. For the sake of clarity, these definitions will be repeated in Chap. 9, dealing with the techniques used to diagnose and classify breathing disturbances in HF.

A reduction ≥90 % of airflow, compared to baseline, and lasting for ≥10 s is named apnea. The apneas can be central (in case of the contextual absence of airflow and respiratory movements), obstructive (when the absence of airflow is coupled to the presence of thoracic and abdominal movements), or mixed (usually starting as central apnea and ending as obstructive) [21].

A hypopnea is defined as a reduction of airflow ≥30 % for ≥10 s, together with either ≥3 % arterial oxygen desaturation or an arousal; a distinction between central and obstructive hypopneas is not usually performed, albeit being relevant from a pathophysiological point of view [21].

The respiratory disturbance index (RDI) corresponds to the average number of apneas, hypopneas, and respiratory event-related arousals per hour of sleep; its calculation requires an EEG recording and then the use of PSG. The diagnosis of OSAS is made when a RDI cut-off (usually ≥10) is reached [21].

The apnea-hypopnea index (AHI) is calculated as the number of apneas and hypopneas per hour of estimated sleep time. AHI values are categorized as normal (0–4), mild sleep apnea (5–14), moderate sleep apnea (15–29), and severe sleep apnea (≥30) [21].

PB is a pattern of periodical waxing and waning of tidal volume characterized by hypopneas and an AHI ≥ 15. As stated above, when central apneas are present, the proper definition is CSR [22].