The bottom line is we have at least 12 more months of this incredible demand for ResMed products.
I'm very proud of 8,000 ResMedians serving patients in 140 countries worldwide.
1 priority will always be patients, doing our best to help those who suffer from sleep apnea, COPD, asthma and other respiratory chronic diseases, as well as those who benefit from our out-of-hospital healthcare software solutions.
We are still seeing a divergence in the total patient flow from 85% to 100% of pre-COVID levels in most countries and above 100% of pre-COVID levels in a few locations.
1 is to grow and differentiate our core sleep apnea, COPD and asthma businesses; No.
2 is to design, develop and deliver world-leading medical devices as well as digital health solutions that can be scaled globally; and No.
3 is to innovate and grow the world's best software solutions for care delivered outside the hospital and especially in the home.
launch of our next-generation device platform called AirSense 11 continues to go very well.
We expect to introduce the AirSense 11 platform into additional countries throughout calendar year 2022.
In parallel, we will continue to sell our globally available market-leading platform, the AirSense 10, to maximize the total volume of CPAP, APAP and bilevels available for sale.
In fact, the only product that the AirSense 10 is inferior to is the AirSense 11.
As you saw in our results with double-digit growth this quarter, the ongoing adoption of both the AirSense 10 and AirSense 11 platforms remains very, very strong.
With the AirSense 11 platform and our digital health technology ecosystem, we are engaging patients in their therapy digitally like never before in the industry.
We have peer-reviewed published evidence showing that combining AirSense platform with myAir software and AirView software, we see over 87% adherence to positive airway pressure therapy.
This was in the study with over 85,000 patients.
On our latest and greatest platform, the AirSense 11, we are driving even higher adoption rates of the myAir app than ever before.
We saw this demonstrated in the Alaska study in partnership with the French healthcare systems, where we showed in a study with over 176,000 patients that those patients who had adhered to CPAP therapy had a 39% relative reduction in mortality rates versus control.
Let me now turn to a discussion of our Respiratory Care business, focusing on our strategy to better serve the 380 million patients with chronic obstructive pulmonary disease or COPD worldwide, and the 330 million patients that suffer from asthma worldwide.
1 issue reported across our customer base, which is staffing challenges.
And we are set up for sustainable growth through ongoing investments in R&D to the tune of 7% of our revenues, commercial excellence in partnerships with CVS, Verily and beyond, as well as future acceleration through strategic M&A, as well as tuck-in M&A as we move forward.
We are transforming out-of-hospital healthcare at scale, leading the market in digital health technology with over 10.5 billion nights of medical data in the cloud and over 16 million 100% cloud connectable medical devices on bedside tables in 140 countries worldwide, we are unlocking value by using de-identified data to help patients, providers, physicians, payers and in entire healthcare systems.
Our mission to improve 250 million lives through better healthcare in 2025, drives and motivates ResMedians every day.
Before I hand the call over to Brett for his remarks, I want to once again express my sincere gratitude to more than 8,000 ResMedians for their perseverance, hard work and dedication during these ongoing unprecedented times.
Group revenue for the December quarter was $895 million, an increase of 12%.
In constant currency terms, revenue increased by 13%.
In relation to the impact of our competitors' recall, we estimate that we generated incremental device revenue in the range of $45 million to $55 million in the December quarter.
For the first half of FY '22, this reflects incremental revenue in the range of $125 million to $145 million.
We continue to expect component supply constraints will limit the total incremental device revenue opportunity to somewhere between $300 million and $350 million for the full fiscal year 2022.
Looking at our geographic revenue distribution and excluding revenue from our Software as a Service business, sales in U.S., Canada and Latin America countries increased by 14%.
Sales in Europe, Asia and other markets increased by 12% in constant currency terms.
By product segment, Globally, in constant currency terms, device sales increased by 16%, while masks and other sales increased by 10%.
Breaking it down by regional areas, device sales in the U.S., Canada and Latin America increased by 19%, as we benefited from incremental revenue due to a competitor's recall and favorable product mix as we sold an increased proportion of higher acuity devices.
Masks and other sales increased by 9%, reflecting solid resupply revenue and achieved despite the challenging device supply environment, which continues to limit new patient setups.
In Europe, Asia and other markets, device sales increased by 13% in constant currency terms, again reflecting the benefit from incremental revenue due to a competitor's recall.
Masks and other sales in Europe, Asia and other markets benefited from improved patient flow relative to the prior year and increased by 11% in constant currency terms.
Software as a Service revenue increased by 8% in the December quarter.
As I stated earlier, we continue to expect component supply constraints will limit the incremental device revenue resulting from our competitors' recall to somewhere between $300 million and $350 million for fiscal year '22.
Our non-GAAP gross margin declined by 230 basis points to 57.6% in the December quarter.
G&A expenses for the second quarter increased by 9% or in constant currency terms increased by 10%.
Importantly, SG&A expense as a percentage of revenue improved to 20.7% compared to 21.2% in the prior year period.
Looking forward and subject to currency movements, we expect SG&A expense as a percentage of revenue to be in the range of 20% to 22% for the second half of FY '22.
R&D expenses for the quarter increased 14% on both a headline and a constant currency basis.
R&D expenses as a percentage of revenue was 7% compared to 6.9% in the prior year quarter.
Looking forward and subject to currency movements, we expect R&D expenses as a percentage of revenue to be in the vicinity of 7% for the second half of FY '22.
Our non-GAAP operating profit for the quarter increased by 5%, underpinned by strong revenue growth, partially offset by the contraction of our gross margin.
On a GAAP basis, our effective tax rate for the December quarter was 15%, while on a non-GAAP basis, our effective tax rate for the quarter was 15.6% compared to the prior year quarter of 15.2%.
Looking forward, we estimate our non-GAAP effective tax rate for the full fiscal year '22 will be in the range of 19% to 20%.
Our non-GAAP net income for the quarter increased by 5% and our non-GAAP diluted earnings per share for the quarter increased by 4%.
Our cash flow from operations for the quarter was $220 million, reflecting robust underlying earnings, partially offset by higher working capital.
Capital expenditure for the quarter was $30 million.
Depreciation and amortization for the quarter totaled $41 million.
During the quarter, we paid dividends to shareholders totaling $61 million.
We recorded equity losses of $1.9 million in our income statement in the December quarter associated with the Primasun joint venture with Verily.
We expect to record equity losses of approximately $2 million per quarter through the balance of fiscal year '22 associated with the joint venture operation.
We ended the second quarter with a cash balance of $194 million.
At December 31, we had $680 million in gross debt and $486 million in net debt.
And at December 31, we had approximately $1.6 billion available for drawdown under our existing revolver facility.
Our board of directors today declared a quarterly dividend of $0.42 per share, reflecting the board's confidence in our operating performance.

Summary:
Group revenue for the December quarter was $895 million, an increase of 12%.