Nocturnal asthma

Computerized capnography allows nocturnal asthma assessment.

Example 1 : Nocturnal monitoring of S3 (22h - 8h)

Peaceful sleep till 4h30, then onset of infra-clinical bronchospasm leading to waking at 5h.
6h : worsening requiring inhalation of a beta-mimetic drug, improvement allowing sleep.
7h : recurring attack leading to complete and breathless wakening at 8h.

Reliability also allows comparative drug challenge tests performed during sleep.

Example 2 : Drug trial in managing severe nocturnal asthma

Recording of 2 successive nights (N1 and N2) each preceded by a distinct treatment (pirbuterol or pirbuterol + salmeterol). Continuous monitoring of index S2 (n<0.30%/sec).Blue trends : Inhalation of pirbuterol at 20h.
Continuous breathlessness (despite additional inhalations at 21h50, 0h40 and 7h00). Note onset then spontaneous improvement of two attacks (3h and 5h). The patient experienced very little sleep..
Green trends : Inhalation of pirbuterol + salmeterol at 20h.
Generally peaceful night (no additionnal inhalation), slight worsening towards morning but patient slept well. N.B. : PEF at bedtime (20 h) was significantly different (N1 : 150, N2 : 250).

Conclusion :

Capnography allows reliable continuous assessment of nocturnal asthma.

Its only weakness relates to REM stages often responsible for bronchospasm-like deformations of the waveform. However, these stages may be detected using "spirometric" parameters (expiration length variability, PetCO2 variability etc...) of which REM influences are characteristic. These parameters are measurable on capnographic waveform, their monitoring was therefore added to shape indices in the software process.