95% of patients achieved an AHI of less than 10, and sleep time remains steady with the pretreatment mean sleep time of 412 minutes compared with 401 minutes of mean sleep time with the ProSomnus EVO device. Compliance was 100% at three month follow-up. Our product differentiation and scientific efforts are reflected in our recent 510(k) premarket notification to the FDA to expand the labeling for use of our EVO precision devices. We submitted what we believe to be a strong data set demonstrating efficacy well above other approved treatments for severe OSA, including HNS and orthodontic devices with what we believe to be far superior safety. Our revised data set, including 74 patients with severe OSA creates a compelling justification for use in this expanded population of patients.
We are actively working through the FDA process and we’ll provide updates as we progress. Continuous nightly oxygen monitoring is the future of Sleep Medicine. Continuous oxygen monitoring is to sleep apnea what continuous glucose monitoring is to diabetes. Clinical studies have demonstrated that sleep apnea-specific hypoxic burden which is derived from continuous oxygen monitoring is predictive of all cause morbidity and mortality, cardiovascular events, heart failure and overall health risk. To this end, ProSomnus demonstrated technical feasibility of our next-generation RPMO2, remote patient monitoring of oxygen device, data from our recently completed pilot study at the University of Calgary Medical Center validated that an oximeter embedded in a ProSomnus EVO precision oral device can indeed accurately, safely, and continuously monitor SpO2, pulse rate, nightly use time and more.
We expect to complete our full FDA test and apply for FDA clearance later this year. We fully expect the ProSomnus RPMO2 device to enable sleep medicine providers to manage their OSA patients according to psychological or physiologic parameters that are indicative of health risk to improve disease management and reduce the cost of care. Next, I’d like to share a few words about meaningful tailwinds that are helpful to ProSomnus’ mission. Several industry developments represent important immediate tailwinds and our long-term structural opportunities for ProSomnus. CPAP recalls persist, creating immediate opportunities for non-CPAP therapies like ProSomnus. Philips, ResMed and SoClean have been hit with involuntary and voluntary FDA recalls. As you know, Philips Respironics has completely shut down its sleep and respiratory medicine businesses affecting an estimated 5 million people alone.
In addition to CPAP recalls, a recent study published in Lancet titled “CPAP May Promote an Endothelial Inflammatory Milieu in Sleep Apnea After Coronary Revascularization”, concludes that greater CPAP levels increased pro-inflammatory lung effects, reduced cardioprotective effects and may counteract benefits of treating OSA with CPAP. The consensus opinion seems to be, and in our opinion is that the GLP-1s and other pharmaceutical treatments for sleep apnea will be net favorable for noninvasive efficacious treatments such as ProSomnus as these pharmaceuticals deliver more patients into the OSA treatment window for ProSomnus. Lastly, the UnitedHealthcare policy establishes an adequate trial of oral appliances as a prerequisite for hypoglossal nerve stimulation treatment.
Although it remains to be seen how this will be handled in clinical practice, this policy decision legitimizes custom oral appliances like ProSomnus as a safe, effective noninvasive mainstream treatment modality. As we drive our business towards our vision with the profitable growth stance, ProSomnus continues to make progress on strengthening our balance sheet. Brian will expand on our balance sheet strengthening activities in the following section. With that, I’d like to turn the call over to Brian Dow, our Chief Financial Officer for a review of our financials. Brian?
Brian Dow: Great. Thanks, Len, and thanks to all of you for joining the call today. The fourth quarter of 2023 was another record-breaking quarter with revenues totaling $7.8 million, representing an increase of 35% from the fourth quarter of 2022 and an 11% increase sequentially from the third quarter of 2023. For the full-year 2023, revenues totaled $27.7 million, an increase of 43% from $19.4 million for 2022. Total operating expenses for the fourth quarter were $12.8 million, an increase of 14% compared to $11.3 million for the third quarter of 2023 and an 8.5% increase from $11.8 million reported for the fourth quarter of 2022. On a full-year basis, operating expenses totaled $46.8 million, an increase of 51.5% from $30.9 million for the full-year 2022.
Operating expenses have been a focal point of attention over the past nine months. As we discussed after the second quarter of 2023, we began transitioning towards streamlining our organization and striking a more balanced profile between growth and the investments needed to achieve such growth. Since that time, our investments in operating expenses have moderated as both a percentage of revenue and from an aggregate dollar standpoint. Cost of revenue has increased relative to increasing production volumes and has also absorbed the impact of higher facility burden and broader economic pricing pressures. Sales and marketing expenses have contracted the levels reported for the fourth quarter and again, on increasing sales volumes and revenues during the period.
Development investments have been balanced relative to key initiatives. And lastly, G&A expenses have moderated but as a public company, we continue to incur the requisite expenses. In addition, during the fourth quarter, we continued to incur the trailing costs from the 2022 leaseback. Looking a little closer at operating expenses for the fourth quarter. Cost of revenue totaled $4.1 million for the fourth quarter ended December 31, 2023 representing 53% of revenue. This reflects an increase of $0.6 million or 15% and $1.4 million or 54% compared to the quarters ended September 2023 and December 2022 respectively. For the full-year 2023, cost of revenue increased to $13.6 million, representing 49% of revenue, an increase of $4.5 million compared to $9.1 million or 47% of revenue for the year ended December 31, 2022.