|M.Sc Student||Yakov Tsibulsky|
|Subject||Non-invasive Monitoring of Patients with Heart Failure by|
Objective Indices of Dyspnea
|Department||Department of Biomedical Engineering||Supervisors||Professor Landesberg Amir|
|Dr. Rispler Shmuel|
Background: Chronic heart failure (HF) affects close to five million Americans and is associated with high rate of recurrent hospitalizations. Even worse is the high rate (27%) of re-hospitalizations within the first 30 days post discharge. The leading symptom for hospitalizations is dyspnea. Currently, there is no precise, validated, quantitative and objective method for assessing dyspnea in HF patients. Dyspnea due to cardiac decompensation is associated with changes in the respiratory efforts that are reflected in the respiratory dynamics.
Purpose: We hypothesize that quantification of the respiratory effort can provide pathognomonic features that measure the severity of cardiac decompensation and may provide precise and objective measures for the effectiveness of the treatment. Moreover, monitoring these changes in chest wall dynamics may provide early non-invasive signs for cardiac decompensation.
Methods: We conducted a clinical trial, in which we measured the breath dynamics of electively hospitalized HF patients. We measured and compared breath dynamics close to admission and at discharge. The study included seventeen patients with decompensated HF (NYHA 3-4) who were hospitalized with moderate dyspnea. Their mean age was 71.6±9.4 years. The patients had a low ejection fraction (25.3±7.8%) and high BNP levels (1566 ±1182). Three miniature motion sensors, which measure the subsonic respiratory dynamics, were attached to the patient's thorax and epigastrium. The respiratory effort was quantified by time and spectral domain indices of the respiratory dynamics signals. A novel parameter, denoted as Excessive Effort Index (EEI) was defined as the ratio between the additional excessive energy and the energy at the basic respiratory rate. The effect of treatment was assessed by calculating the change in EEI between admission and discharge (∆EEI).
Results and discussion: Patients with decompensated HF had a polyphasic breath with mild increase in breath rate and a prominent active expiration. The active expiration and the vigorous inspiratory phase yielded polyphasic motion of the chest and the abdomen. Reduction in body weight and changes in breath rate poorly predicted the rate of rehospitalization. However, significant reduction in EEI was associated with low rate of readmission due to HF during the first month post hospital discharge (p<0.01). A value of EEI<0.4 provided 100% differentiation between those who were re-hospitalized within 30 days and those with prolonged freedom from readmission. Moreover, we have identified four different types of breathing: 1 - Normal, 2 - Active Expiration, 3 - Excessive Expiratory work, and 4 - Periodic breathing. The changeover from one type to the following type was related to aggravation in the cardiac decompensation, while stepping downward was associated with a relief in severity of cardiac decompensation.
Conclusions: Quantification of the respiratory effort provides objective indices for monitoring patients with decompensated HF. Novel pathognomonic signs of dyspnea due to cardiac decompensation have been revealed and described. The excessive energy due to additional expiratory work correlates with the severity of cardiac decompensation. The Excessive Effort Index and the four types of breathing can assist in predicting the rate of early (within a month) readmission and in decision making prior to patients' discharge from the hospital.