Catathrenia is Not Expiratory Snoring

WE THANK VETRUGNO ET AL1 FOR THEIR COMMENTS IN RESPONSE TO OUR MANUSCRIPT. WE AGREE THAT CATATHRENIA SHOULD NOT BE CONFUSED WITH expiratory snoring. However, we strongly disagree with their erroneous presumption that our findings represent snoring—an argument which they have based entirely on differences in microphone display collected by two different methods. Our two groups share a similar lapse in that neither was precise about how this sound was truly monitored, processed, or displayed in the respective figures. Catathrenia is not common and prior to our manuscript we accumulated only 6 cases over the previous five years.2 Our catathrenia patients had home recordings of their conspicuous and “bizarre” sounds convincing us of the originality of their problem during their initial clinic consultation. These sounds were distinctly different expiratory sounds that could not be confused with expiratory snoring. Once in the laboratory our patients were monitored by audio speaker in real time providing observers undeniable confirmation of the distinct quality of their groaning sounds. This was neither recorded nor displayed in our montage. We did present a microphone signal in our published report. This signal was digitized and presented as a visual display in our routine clinical fashion. This microphone is placed for the detection of routine snoring and not for the purpose of complex acoustic analysis nor with the intent of providing a signal that clearly discriminates snoring from expiratory groaning. Due to variability in placement and equipment, even duration of the sound may not be comparable; and as our colleagues know, duration is variable throughout the night. We have been involved in acoustic analysis previously. We know that these analyses require a more sophisticated and well-defined technique. The “microphone,” its properties, its specific and reproducible location on the subject, recording, processing, and displaying technique all need to be defined.3 As acoustic analysis of this signal was not intended at the time of collection or reporting in our catathrenia manuscript, we neglected these details. Our Italian colleagues subsequently repeated this error. Such analysis was not within the scope of our investigation and had not been done in any prior article on catathrenia. Both our groups presented figures obtained during the monitoring of subjects that undeniable displayed nocturnal groaning distinct from expiratory snoring. Both groups however only indicated the variable monitored. If we look at the presented figures placed in the commentary by Vetrugno et al., a recording is presented with an undefined microphone, without description of its sound characteristics, placed in an undefined position compared to the sleeping subject, with a presentation of a signal recorded with an undefined unit on an undefined system, without any of the necessary information to perform a critical acoustic analysis. Many technical details are omitted in articles presenting segments of polysomnographic recordings, and this is the case in both ours and our Italian colleagues' figures. Our study was performed using two different means for the investigation of the subject behavior and presence of sound during sleep. For determination of the timing of the sound compared to respiratory cycle, we used a piezo sensor located on the lateral side of the neck roughly in a similar location between patients, but without a defined relationship to anatomical landmarks. This sensor gives a signal with a known power. It is calibrated in an artificial unit on a computerized system (Sandman, Ontario, Canada) before any recording and bio-calibration are obtained by having subjects perform specific, standardized sounds, which are not measured for volume or pitch. It is called a “neck microphone,” but this equipment does not generate the more complex shape of a sound, as would a directional microphone placed perpendicular to the nose of the subject at a 60-cm distance, monitored with a signal calibrated in decibel on a specific recorder for that purpose. In our study, we also used a multi-directional microphone, placed on the night stand of the patient, which means a variable lateral distance depending of the subject position that may vary from 1 to 2 meters during the night, with sounds transmitted through an interphone to a recording room without direct recording on polysomnography but with human monitoring in association with continuous videotaping. Home investigations used commercially available tape recorders with a standard decibel range (usually 40-120 dB) placed in the subject bedroom. These systems allow discrimination of snoring from other types of sound, identification of respiratory phase of the sound, and the relationship to sleep stages. None of these techniques are appropriate for a more sophisticated physical analysis of the sound or comparison between varied methodologies. If a special effort is not made to monitor the obtained signal specifically for such analysis, it will be difficult to draw conclusions or compare between studies.3 We did not attempt to make such conclusions or comparisons, but Vetrugno et al have. Additional reports are forthcoming from the Mayo clinic with a case-report recently published in Sleep Medicine4 and an abstract in press5 presenting 11 cases to be presented at the 2008 SLEEP meeting. These present catathrenia similar to ours with sounds observed during both NREM and REM sleep and associated with sleep disordered breathing. They also used nasal CPAP in patients with OSA and report similar improvement as we observed in our own cases.