Laser measurement of respiration activity in preterm infants: Monitoring of peculiar events

The Neonatal Intensive Care Unit (NICU) is a part of a pediatric hospital dedicated to the care of ill or pre-term patients . NICU's patients are underweight and most of the time they need cardiac and respiratory support therapies; they are placed in incubators or in cribs maintaining target environmental and body temperatures and protecting patients from bacteria and virus. Patients are continuously monitored for long period of time (days or weeks) due to their possible several health conditions. the most common vital signs monitored are: respiration rate, heart rate, body temperature, blood saturation, etc. Most of the devices used for transducing such quantities in electronic signals - like spirometer or electrocardiogram (ECG) - are in direct contact with the patient and results, also in consideration of the specific patient, largely invasive. In this paper, we propose a novel measurement system for non-contact and non-invasive assessment of the respiration activity, with particular reference to the detection of peculiar respiration events of extreme interest in intensive care units, such as: irregular inspiration/expiration acts, hiccups and apneas. The sensing device proposed is the Laser Doppler Vibrometer (LDVi) which is an non contact, optical measurement system for the assessment of a surface velocity and displacement. In the past it has been demonstrated to be suitable to measure heart rate (HR) and respiration rate (RR) in adult and in preterm infant trough chest-wall displacements. The measurement system is composed by a LDVi system and a data acquisition board installed on a PC, with no direct contact with the patient. Tests have been conducted on 20 NICU patients, for a total of 7219 data sampled. Results show very high correlation (R=0.99) with the reference instrument used for the patient monitoring (mechanical ventilator), with an uncertainty < ±7 ms (k=2). Moreover, during the tests, some peculiar respiration events, have been recorded on 6 of the monitored patients: irregular inspiration/expiration acts (4), hiccups (1) and apneas (1). The proposed measurement method shows to be able to precisely detect the instantaneous respiration frequency of the patient, avoiding patient contact. Moreover the signal collected allow to identify irregularities in the patient respiration of different severity, allowing an optimized action of the care givers.