Cervical spondylosis as a possible hidden reason beyond delayed phrenic nerve distal motor latency
Authors: Rowaida Hamdy Ali, Mai Mohamed Farouk and Salwa Galal Moussa
DOI / Source: https://doi.org/10.1186/s43166-020-00051-0
Date: December 2021
Reading level: Intermediate
Why This Matters for Freedivers
Freediving depends heavily on diaphragm control, comfortable breathing mechanics, and efficient recovery breathing — and this paper suggests that “neck issues” can quietly affect the nerve supply to the diaphragm in some people. If a diver has unexplained breathlessness on exertion, reduced ventilation power, or odd diaphragm fatigue (especially with significant neck degeneration), it’s a reminder that the problem might not be in the lungs — it might be in the phrenic nerve pathway, which is worth medical evaluation.
Synopsis
Most freedivers focus on lungs, CO₂, and relaxation — but there’s another piece of the breathing system that’s easy to forget: the wiring. Your diaphragm (the main breathing muscle) is controlled by the phrenic nerve, which comes from the neck (mainly the C3–C5 nerve roots, especially C4). This paper asks a quiet but important question: can common “wear-and-tear” changes in the neck (cervical spondylosis) subtly slow phrenic nerve signals, even before someone has obvious breathing problems? 
The researchers compared 30 people with cervical spondylosis above C5 (neck pain, degenerative changes seen on X-ray) with 30 healthy controls. They did phrenic nerve conduction studies on both sides — basically an electrical stimulation test to see how quickly the nerve triggers the diaphragm response. The main measurement was distal motor latency (DML): how long the signal takes to get from stimulation point to the muscle response. 
The result was clear: people with cervical spondylosis had a significantly longer phrenic nerve latency on both sides than the healthy group, meaning the nerve signal was slower. The amplitude (roughly, the size/strength of the response) wasn’t significantly different overall, which suggests the nerve wasn’t “dead” — it was more like a conduction delay, consistent with mild demyelination/compression effects. Even more interesting: the delay correlated with how severe the degenerative changes were on X-ray (higher X-ray scores tended to mean more latency). In short, cervical spondylosis may be an under-recognized reason for subtle phrenic nerve impairment, and the worse the neck degeneration, the more likely the delay.
Abstract
Background: Cervical spondylosis is a chronic degenerative condition of the cervical spine that can affect the cervical nerve roots. The origin of the phrenic nerve makes it vulnerable to injury. The purpose of this study is to investigate possible subtle phrenic nerve affection in patients with cervical spondylosis using nerve conduction studies (NCS). This study was conducted on 30 patients with cervical spondylosis above C5 and on 30 healthy volunteers. Nerve conduction studies of both phrenic nerves were performed in all cases.
Results: The patients with cervical spondylosis showed a statistically highly significant prolongation of phrenic nerve distal motor latency (DML) than the control group (P < 0.01). There was no significant difference regarding amplitude (P > 0.05). There was a significant correlation between DML and X-ray score (r < 0.05).
Conclusions: Cervical spondylosis is an underestimated cause of phrenic nerve delayed DML. There is a correlation between the delay of phrenic nerve DML and the severity of cervical spondylosis.